opentui(phase3): launcher integration — HERMES_TUI_ENGINE dual-engine

hermes --tui launches the native OpenTUI engine (Bun) when
HERMES_TUI_ENGINE=opentui (env) or display.tui_engine=opentui (config);
Ink stays the default and the shipping path is untouched.

- _resolve_tui_engine() (env > config > ink); refuses opentui on
  Windows/Termux (no Bun) -> falls back to ink with a notice.
- _make_opentui_argv() -> [bun, src/entry.real.tsx] (no build step).
- _bun_bin() with HERMES_BUN override.
- Branch at top of _make_tui_argv BEFORE _ensure_tui_node (Bun-only host
  must not bootstrap Node).
- Gate _launch_tui NODE_OPTIONS/--max-old-space-size on engine==ink (Bun
  is JSC; the V8 flag errors/ignores).

Verified end-to-end via tmux: real hermes --tui -> Bun -> OpenTUI ->
real Python gateway streamed a real reply. No-flag default still ink.

apps/desktop/src/styles.css

@@ -5,10 +5,6 @@
 @import '@vscode/codicons/dist/codicon.css';
 @custom-variant dark (&:is(.dark *));
 
-/* Sidebar sections: tall viewports give each its own scroller; compact ones
-   (this variant) flatten everything into one shared scroll. See ChatSidebar. */
-@custom-variant compact (@media (max-height: 768px));
-
 @font-face {
   font-family: 'Collapse';
   font-style: normal;
@@ -17,30 +13,6 @@
   src: url('../../../node_modules/@nous-research/ui/dist/fonts/Collapse-Bold.woff2') format('woff2');
 }
 
-/* JetBrains Mono — bundled terminal font (Apache-2.0) so bold/italic share the
-   regular face's metrics instead of squeezing against a system fallback. */
-@font-face {
-  font-family: 'JetBrains Mono';
-  font-style: normal;
-  font-weight: 400;
-  font-display: swap;
-  src: url('./fonts/JetBrainsMono-Regular.woff2') format('woff2');
-}
-@font-face {
-  font-family: 'JetBrains Mono';
-  font-style: normal;
-  font-weight: 700;
-  font-display: swap;
-  src: url('./fonts/JetBrainsMono-Bold.woff2') format('woff2');
-}
-@font-face {
-  font-family: 'JetBrains Mono';
-  font-style: italic;
-  font-weight: 400;
-  font-display: swap;
-  src: url('./fonts/JetBrainsMono-Italic.woff2') format('woff2');
-}
-
 @theme inline {
   --color-background: var(--dt-background);
   --color-foreground: var(--dt-foreground);
@@ -294,12 +266,10 @@
     --dt-user-bubble: var(--ui-chat-bubble-background);
     --dt-user-bubble-border: var(--ui-stroke-tertiary);
 
-    --dt-font-sans:
-      'Segoe WPC', 'Segoe UI', -apple-system, BlinkMacSystemFont, 'SF Pro Text', system-ui, sans-serif,
+    --dt-font-sans: 'Segoe WPC', 'Segoe UI', -apple-system, BlinkMacSystemFont, 'SF Pro Text', system-ui, sans-serif,
+      'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol', 'Noto Color Emoji', emoji;
+    --dt-font-mono: 'Cascadia Code', 'JetBrains Mono', 'SF Mono', ui-monospace, Menlo, Consolas, monospace,
       'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol', 'Noto Color Emoji', emoji;
-    --dt-font-mono:
-      'Cascadia Code', 'JetBrains Mono', 'SF Mono', ui-monospace, Menlo, Consolas, monospace, 'Apple Color Emoji',
-      'Segoe UI Emoji', 'Segoe UI Symbol', 'Noto Color Emoji', emoji;
     --dt-base-size: 1rem;
     --dt-line-height: 1.5;
     --dt-letter-spacing: 0;
@@ -847,37 +817,6 @@ canvas {
    content's --message-text-indent). No extra prose indent — a single gutter
    reads cleaner than a ragged tool-vs-reply column. */
 
-/* RTL/bidi chat text (#44150): each block resolves its own base direction from
-   its first strong char (UAX#9 plaintext). text-align:start makes that resolved
-   direction drive alignment too — load-bearing, since the user bubble pins
-   text-left. direction is never set, so chrome/layout/list-indent stay LTR (the
-   issue asks not to flip the whole UI). Covers assistant prose, user lines, and
-   both composers (main + edit share composer-rich-input). */
-[data-slot='aui_assistant-message-content'] .aui-md :where(p, h1, h2, h3, h4, h5, h6, li, blockquote),
-[data-slot='aui_user-inline-text'],
-[data-slot='composer-rich-input'] {
-  unicode-bidi: plaintext;
-  text-align: start;
-}
-
-/* Inline code/KaTeX don't vote on direction and keep their own order: isolate
-   makes bidi treat each as one neutral, so a block that *starts* with `./run.sh`
-   then Arabic still resolves RTL, and the command's neutrals (dots/slashes)
-   aren't reordered by the surrounding RTL run. */
-[data-slot='aui_assistant-message-content'] .aui-md :where(:not(pre) > code),
-[data-slot='aui_user-inline-code'],
-[data-slot='aui_assistant-message-content'] .aui-md .katex {
-  direction: ltr;
-  unicode-bidi: isolate;
-}
-
-/* Fenced code stays LTR even inside an RTL list item/blockquote — never mirrors. */
-[data-slot='aui_assistant-message-content'] .aui-md [data-slot='code-card'],
-[data-slot='aui_user-fence'] {
-  direction: ltr;
-  text-align: left;
-}
-
 [data-slot='aui_user-message-root'] {
   top: var(--sticky-human-top);
 }
@@ -975,11 +914,7 @@ canvas {
 
   display: block;
   inline-size: var(--fit-available-space);
-  font-size: clamp(
-    var(--fit-min, 1em),
-    1em * var(--fit-ratio),
-    var(--fit-max, infinity * 1px) - var(--fit-support-sentinel)
-  );
+  font-size: clamp(var(--fit-min, 1em), 1em * var(--fit-ratio), var(--fit-max, infinity * 1px) - var(--fit-support-sentinel));
 }
 
 @container (inline-size > 0) {