Merge upstream PR 21st-dev#195: UI Sidebar + Chat Overhaul

Big upstream change set merged on top of our local fork:

- Sidebar architecture rework (project-grouped tree, expandable workspaces,
  SubChatItem component, sort popover, Tabler icons, footer "Open Workspace"
  button replacing the old Settings/Kanban/Archive triplet)
- Chat font size setting (12-16px) with em-based markdown scaling
- Terminal font size setting (10-24px) with dynamic line-height
- Workspace accent colors + DB migration 0008 (chats.accentColor)
- DB migration 0009
- active-chat.tsx split into chat-utils.tsx + diff-sidebar-section.tsx
- TypeScript strictness fixes across routers, hooks, and dialogs
- New deps: @tabler/icons-react, react-grab, sharp

Conflict resolution: agents-sidebar.tsx had 5 conflict regions vs our
PR 21st-dev#192 ChatIcon/ProjectIcon work - took upstream since the new sidebar
design intentionally drops the GitHub-avatar default and our PR 21st-dev#192's
intent (no GitHub logo for local chats) is achieved by upstream's redesign.

Preserved our local-only customizations:
- Auth bypass in auth-manager.ts (isAuthenticated -> true, stub user)
- main window loads index.html unconditionally (no login route)
- Help/Feedback buttons gone (upstream's new footer is a single Open
  Workspace button, no Help/Feedback present)
- Opus 4.7 + opus[1m] model entries
- RenderErrorBoundary wrappers around 3 ChatViewInner instances
- setTimeout(100ms) focus fix for terminal -> chat handoff

Author: erenbertr

CLAUDE.md

@@ -79,7 +79,7 @@ src/
         ├── atoms/           # Global Jotai atoms
         ├── stores/          # Global Zustand stores
         ├── trpc.ts          # Real tRPC client
-        └── mock-api.ts      # DEPRECATED - being replaced with real tRPC
+        └── api-bridge.ts    # Wraps tRPC calls + stubs for web-only features
 ```
 
 ## Database (Drizzle ORM)
@@ -243,7 +243,6 @@ npm version patch --no-git-tag-version  # 0.0.27 → 0.0.28
 - tRPC routers structure
 
 **In Progress:**
-- Replacing `mock-api.ts` with real tRPC calls in renderer
 - ProjectSelector component (local folder picker)
 
 **Planned:**

build/icon-blue-original.png

@@ -0,0 +1 @@
+ALTER TABLE `chats` ADD `accent_color` text;

build/icon.icns

@@ -0,0 +1 @@
+ALTER TABLE `projects` ADD `accent_color` text;