Refine Foundry UI layout and styling (#235)

* feat: modernize chat UI and rename handoff to task

- Remove agent message bubbles, keep user bubbles (right-aligned)
- Rename "Handoffs" to "Tasks" with ListChecks icon in sidebar
- Move model picker inside composer, add renderFooter to ChatComposer SDK
- Make project sections collapsible with hover-only chevrons
- Remove divider between chat and composer
- Update model picker chevron to flip on open/close
- Replace all user-visible "handoff" strings with "task" across frontend

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: real org mock data, model picker styling, project icons, task minutes indicator

- Replace fake acme/* mock data with real rivet-dev GitHub org repos and PRs
- Fix model picker popover: dark gray surface with backdrop blur instead of pure black
- Add colored letter icons to project section headers (swap to chevron on hover)
- Add "847 min used" indicator in transcript header
- Rename browser tab title from OpenHandoff to Foundry
- Reduce transcript header title font weight to 500

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: refine Foundry UI — single-line task cards, dark user bubbles, curved panel corners, send icon

- Collapse task sidebar cards to single-line layout (title, number, diffs, timestamp)
- Dark-themed user message bubbles matching site theme
- Curved top-left corner on center chat panel with border line
- Subtle focus border on composer input
- Replace ArrowUpFromLine with SendHorizonal icon
- Tab strip gaps, padding, and divider alignment fixes
- Plus button with visible background
- Right sidebar header color matching

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

factory/packages/frontend/src/app/theme.ts

@@ -4,15 +4,15 @@ export const appTheme: Theme = createDarkTheme({
   colors: {
     primary: "#e4e4e7", // zinc-200
     accent: "#ff4f00", // orange accent (inspector)
-    backgroundPrimary: "#000000", // pure black (inspector --bg)
-    backgroundSecondary: "#0a0a0b", // near-black panels (inspector --bg-panel)
-    backgroundTertiary: "#0a0a0b", // same as panel (border provides separation)
+    backgroundPrimary: "#09090b", // darkest — chat center panel
+    backgroundSecondary: "#0f0f11", // slightly lighter — sidebars
+    backgroundTertiary: "#0c0c0e", // center + right panel headers
     backgroundInversePrimary: "#fafafa",
     contentPrimary: "#ffffff", // white (inspector --text)
     contentSecondary: "#a1a1aa", // zinc-400 (inspector --muted)
     contentTertiary: "#71717a", // zinc-500
     contentInversePrimary: "#000000",
-    borderOpaque: "rgba(255, 255, 255, 0.18)", // inspector --border
-    borderTransparent: "rgba(255, 255, 255, 0.14)", // inspector --border-2
+    borderOpaque: "rgba(255, 255, 255, 0.10)", // inspector --border
+    borderTransparent: "rgba(255, 255, 255, 0.07)", // inspector --border-2
   },
 });