feat(ui): redesign workspace shell with context panel, tabbed sidebars, and faster diff UX (#433)

* feat: tabbed right sidebar, context panel, floating diff comments

* fix: auto-close left sidebar when context panel opens

- Increase default context panel width from 520 to 600 pixels
- Increase sidebar minimum width from 200 to 300 pixels
- Replace collapsible component with custom button in diff view

* refactoring: rework sidebars, tabs, and file tree layout

- Rewrite AnimatedTabs as segment-style with sliding indicator
- Upgrade SidebarFilesTree to match FilesView features (context menus,
  git status, file icons, CRUD dialogs, fuzzy search ranking)
- Restructure FilesView header: tabs row + actions row, remove breadcrumbs
- Show relative path in context panel header, track active tab
- Allow left sidebar to stay open alongside context panel
- Hide diff/files tabs from header on desktop (mobile-only)
- Move chevron after group name in session sidebar
- Compact tab heights in right sidebar and git view
- Size PreviewToggleButton to match other action buttons
- Remove directory loading spinner from folder icons

* feat: add project icon and color customization

- Enable users to assign custom icons to projects
- Allow users to choose accent colors for projects
- Stabilize repo status UI during project switching

* feat: add scroll fade indicators to editor tabs

* style: reduce spacing and icon sizes in header

* style: adjust tab component padding from uniform to vertical-horizontal

* feat: Add session state indicators to project tabs

* feat: Enhance session status handling and improve UI responsiveness

* fix: preserve upstream tracking on branch rename

* fix: improve initial remote selection for pull requests

- Uses saved remote name from previous session when available
- Selects remote based on tracking branch when possible
- Falls back to origin or first available remote

* perf(diff): faster highlight, stable stacked scroll

- split/unified Pierre worker pools; prefer shiki-wasm
- align diff CSS line-height; disable scroll anchoring; drop WebKit compositing hacks
- harden stacked pin/align (cancel on user scroll/input); prevent overscroll
- make overlay scrollbar MutationObserver optional; disable for diff container

* feat: handle binary files in diff view

* fix: adjust project tabs layout and drag regions

* style: update drag overlay visual styling

* feat: enable number keys to switch projects in the sidebar

* fix: recognize octet-stream as text-based MIME type

* feat: add keyboard navigation to context panel

* feat: add session pinning to sidebar

- Pin important sessions to keep them at the top
- Pinned sessions persist across browser sessions

* refactor: move context usage display from chat input to header

packages/ui/src/styles/design-system.css

@@ -18,7 +18,7 @@
 
     /* Semantic typography defaults (must match SEMANTIC_TYPOGRAPHY) */
     --text-markdown: 0.9375rem;
-    --text-code: 0.9063rem;
+    --text-code: 0.8125rem;
     --text-ui-header: 0.9375rem;
     --text-ui-label: 0.8750rem;
     --text-meta: 0.875rem;