feat(desktop): unified overlay design system, BrandMark & onboarding redesign (#40708)

* fix(desktop): unify dialog/overlay buttons on shared Button component

Replace raw <button> action/text controls across the modal layer (boot
failure, install, update, onboarding, clarify, model-visibility,
notifications, gateway menu) with the shared Button + its variants
(text / ghost / icon-xs). Drops the bespoke square-cornered styling so
every dialog matches the app's slightly-rounded button system, and
swaps clarify-tool's hardcoded "Skip" for the existing i18n string.

* feat(desktop): add dev-only dialog gallery for auditing overlays

A code-split, DEV-gated harness (toggle ⌘/Ctrl+Alt+Shift+D) that triggers
every dialog/overlay so their buttons can be eyeballed in one place:
store-driven overlays (boot failure, updates, notifications, sudo/secret)
plus in-place dialogs (confirm, profile create/rename, attach-url, model
picker/visibility, clarify, tool approval). Never ships to production.

* fix(desktop): use Ctrl+Shift+D for dialog gallery (mac-friendly)

The Cmd/Ctrl+Alt+Shift+D chord is impractical on macOS (Option mangles
the keypress). Ctrl+Shift+D is the same chord on every platform and uses
neither Cmd nor Option.

* fix(desktop): stop overriding button icon size to size-4

Action buttons hardcoded size-4 icons, overriding the Button component's
built-in size-3.5. That extra 2px is why boot-failure / onboarding / gateway
buttons looked chunkier than the settings "Apply" (size-3.5 spinner) despite
being the same component+size. Drop the overrides so icons inherit 3.5.

* feat(desktop): add BrandMark, use it in the updates overlay hero

New BrandMark renders the white logo.png on a hardcoded brand-blue tile
(#0000F2 light / #222 dark), replacing the generic Sparkles hero glyph in
the "update available" overlay. Trying it here first to iterate on the look.

NOTE: apps/desktop/public/logo.png is currently a 1x1 placeholder — the tile
renders now; the glyph appears once the real white logo art is dropped in.

* feat(desktop): add real logo.png asset, render it white in BrandMark

logo.png is blue line-art on transparent, so force it white via filter to
read on both the brand-blue (#0000F2) and near-black (#222) tiles. Bump the
glyph to 62% of the tile for the portrait aspect.

* fix(desktop): BrandMark renders logo as-is, no light bg/radius/padding

Drop the white filter, the hardcoded light-mode blue tile, the radius, and
the inner padding. Logo now fills the tile over a transparent surface in
light mode; dark keeps the #222 tile.

* fix(desktop): bump updates-overlay BrandMark to size-16

* feat(desktop): use downscaled karb.webp in BrandMark

Swap the BrandMark glyph to karb.webp, downscaled from 1129x1418/888KB to
254x320/81KB for the hero badge.

* feat(desktop): use nous-girl mark in BrandMark, invert in dark

Key the white background to transparent so only the black line-art remains
(384px/20KB webp). Light mode shows black art; dark mode flips it white via
dark:invert on the #222 tile. Drop the now-unused karb.webp and logo.png.

* fix(desktop): BrandMark uses nous-girl as-is (no transparent/invert)

The dark-mode invert read as a creepy negative. Use the opaque black-on-white
mark unchanged in both themes; drop the white-key, dark:invert, and #222 tile.

* fix(desktop): give BrandMark an explicit white bg tile

* fix(desktop): use nous-girl.jpg directly in BrandMark

* perf(desktop): downscale nous-girl.jpg to 256x256 (466KB -> 19KB)

* style(desktop): bump nous light --theme-secondary to 14% blue

* fix(desktop): outline button is transparent, not chrome-filled

The outline variant used bg-background (the chrome color), so on cards/overlays
with a different surface it rendered as an odd gray-blue fill (visible on the
boot overlay's Repair install / Use local gateway). Make it bg-transparent so
it inherits the surface like a real outline. Reverts the unrelated
--theme-secondary tweak.

* fix(desktop): clean outline button — thin border, no shadow/fill

Drop shadow-xs and the resting fills (light chrome bg, dark bg-input/30) so
outline is just a thin clean border with a subtle hover, in both themes.

* fix(desktop): stop forcing tertiary bg on outline buttons

A global [data-variant='outline'] rule set background: var(--ui-bg-tertiary),
which (attribute-selector specificity) overrode the cva bg-transparent — so
outline buttons always showed the pale tertiary fill on cards/overlays
regardless of the variant classes. Scope that fill to secondary only; outline
is now a true transparent border.

* style(desktop): unified overlay design system + restore #38631 flat-UI

Overlays/dialogs/toasts share a custom shadow-nous (downward-weighted) and
--stroke-nous hairline instead of hard borders: boot-failure, install,
notifications, model-picker, onboarding, prompt-overlays, updates, Dialog.

- button: outline is a 1px inset ring (no fill/shadow); chrome lives in Button
- BrandMark: 256px nous-girl mark replaces sparkle glyphs (updates/onboarding/about)
- onboarding: conditional header, lemniscate-bloom loaders, OTP device-code boxes,
  NOUS CONNECTED hero (ascii decode) + cuneiform easter egg, "Begin" matrix exit
- shared LogView + ErrorState; math/ascii loaders over "Loading..." text
- appearance-settings flattened to SegmentedControl/ListRow; keybind-panel on
  shadow-nous + text-variant reset
- restore flat-UI clobbered by #38631's stale-squash (4a1907bd1): command-center,
  profiles, skills, messaging, cron de-boxed; shared SearchField + PAGE_INSET_X;
  profiles back on OverlaySplitLayout; skills tabs+search one row, no row dividers

* refactor(desktop): clean pass — drop dead code, dedupe, fix stale docs

- log-view: drop unused `bare` prop + forwardRef (no caller uses ref)
- install-overlay: drop `stateOverride` (only the removed dev gallery used it)
- profiles: ProfilesViewProps down to { onClose } (drop vestigial section/titlebar)
- onboarding: hoist shared PROVIDER_ROW_CLASS (was duplicated 2x)
- brand-mark / error-state: tighten comments, fix stale AlertCircle reference

apps/desktop/src/styles.css

@@ -60,7 +60,6 @@
   --color-sidebar-foreground: var(--sidebar-foreground);
   --color-sidebar: var(--sidebar);
 
-  --shadow-ink: var(--dt-foreground);
   --shadow-xs: 0 0.0625rem 0.125rem color-mix(in srgb, #000 5%, transparent);
   --shadow-sm:
     0 0 0 0.0625rem color-mix(in srgb, var(--dt-foreground) 6%, transparent),
@@ -69,19 +68,24 @@
     0 0 0 0.0625rem color-mix(in srgb, var(--dt-foreground) 8%, transparent),
     0 0.25rem 1rem color-mix(in srgb, #000 8%, transparent),
     0 1rem 2rem -1.5rem color-mix(in srgb, #000 18%, transparent);
+  /* Soft floating shadow for borderless modals/overlays. Single top light
+     source: every layer is centered (x=0) and cast downward, with negative
+     spread that grows with the blur so each layer is pulled horizontally inward
+     — the shadow pools below the panel instead of bleeding out every side.
+     Layered (contact → ambient) for a smooth, natural falloff. */
+  --shadow-nous:
+    0 0.125rem 0.25rem -0.125rem color-mix(in srgb, #000 7%, transparent),
+    0 0.5rem 0.75rem -0.375rem color-mix(in srgb, #000 6%, transparent),
+    0 1.25rem 1.75rem -0.875rem color-mix(in srgb, #000 6%, transparent),
+    0 2.25rem 3rem -1.75rem color-mix(in srgb, #000 0%, transparent);
+  /* Hairline border paired with --shadow-nous on borderless overlays.
+     currentColor resolves per-element, so it adapts to text color/theme. */
+  --stroke-nous: color-mix(in srgb, currentColor 3%, transparent);
   --shadow-lg:
     inset 0 0.0625rem 0 color-mix(in srgb, #fff 28%, transparent),
     0 0 0 0.0625rem color-mix(in srgb, var(--dt-foreground) 8%, transparent),
     0 0.75rem 2rem color-mix(in srgb, #000 12%, transparent);
-  --shadow-header:
-    0 0.0625rem 0 color-mix(in srgb, var(--dt-foreground) 7%, transparent),
-    0 0.625rem 1.5rem -1.25rem color-mix(in srgb, #000 16%, transparent);
   --shadow-composer: 0 0.0625rem 0.125rem color-mix(in srgb, #000 5%, transparent);
-  --shadow-composer-focus:
-    0 0 0 0.125rem color-mix(in srgb, var(--dt-composer-ring) calc(10% * var(--composer-ring-strength)), transparent),
-    0 0 0 0.0625rem color-mix(in srgb, var(--dt-composer-ring) calc(22% * var(--composer-ring-strength)), transparent),
-    0 0.25rem 0.875rem color-mix(in srgb, #000 8%, transparent),
-    0 0.75rem 2rem -1.25rem color-mix(in srgb, #000 14%, transparent);
 }
 
 @layer base {
@@ -610,28 +614,10 @@ button {
   -webkit-app-region: no-drag;
 }
 
-[data-slot='button'] {
-  box-shadow: none;
-  transition-duration: 100ms;
-}
-
-[data-slot='button'][data-variant='outline'],
-[data-slot='button'][data-variant='secondary'] {
-  border-color: var(--ui-stroke-secondary);
-  background: var(--ui-bg-tertiary);
-  color: var(--ui-text-primary);
-}
-
-[data-slot='button'][data-variant='ghost'] {
-  color: var(--ui-text-secondary);
-}
-
-[data-slot='button'][data-variant='outline']:hover,
-[data-slot='button'][data-variant='secondary']:hover,
-[data-slot='button'][data-variant='ghost']:hover {
-  background: var(--chrome-action-hover);
-  color: var(--ui-text-primary);
-}
+/* Button variant styling lives entirely in the cva in components/ui/button.tsx
+   (the single source of truth). Don't re-add [data-slot='button'] rules here —
+   attribute selectors out-specify the Tailwind utilities and silently override
+   the variants. */
 
 [data-slot='dropdown-menu-content'],
 [data-slot='select-content'],