feat(web): add collapsible sidebar for the dashboard (#33421)

* feat(web): add collapsible sidebar for the dashboard

The desktop sidebar can now be collapsed to an icon-only rail via a
toggle button in the sidebar header.  State is persisted in
localStorage so it survives page reloads.

When collapsed (lg+ only):
- Sidebar shrinks from w-64 to w-14 with a smooth width transition
- Nav items show only their icon with a native title tooltip
- Brand text, plugin headings, system actions, theme/language
  switchers, auth widget, and footer are hidden
- Mobile drawer behavior is unchanged (always full-width)

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(web): align sidebar tooltips to sidebar edge consistently

Tooltip left position now uses the sidebar's right edge instead of the
anchor element's right edge, so narrow anchors (theme/language switchers)
align with full-width anchors (nav links, system actions).

Co-authored-by: Cursor <cursoragent@cursor.com>

* feat(web): add tooltip animations, restore theme label, rename Sessions tab

- Sidebar tooltips now animate in with a subtle 120ms ease-out slide;
  subsequent tooltips within the same hover sequence appear instantly
  (no delay/animation) following Emil Kowalski's tooltip pattern
- Restore theme name label when sidebar is expanded
- Rename Sessions segment tab to "History" across all 16 locales

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(web): smooth sidebar collapse animation

- Remove icon centering on collapse; icons stay left-aligned at px-5
  so they don't jump during the width transition
- Text labels fade out with opacity transition instead of instant
  display:none, clipped naturally by overflow-hidden
- Slow collapse duration from 450ms to 600ms for a more relaxed feel
- Gateway dot always rendered with opacity toggle so it doesn't
  slide in from the right on collapse
- Pin gateway dot at fixed left offset (pl-[1.625rem]) to align
  with nav icons
- Align header toggle button with justify-center when collapsed
- Bottom switchers use items-start when collapsed to prevent reflow

Co-authored-by: Cursor <cursoragent@cursor.com>

---------

Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/index.css

@@ -170,6 +170,12 @@ code { font-size: 0.875rem; }
 }
 
 
+/* Collapsed sidebar tooltip entrance — skipped when moving between items. */
+@keyframes sidebar-tooltip-in {
+  from { opacity: 0; transform: translateY(-50%) translateX(-4px); }
+  to   { opacity: 1; transform: translateY(-50%) translateX(0); }
+}
+
 /* Toast animations used by `components/Toast.tsx`. */
 @keyframes toast-in {
   from { opacity: 0; transform: translateX(16px); }