feat: v0.12.0 — fix streaming tool UI persistence, file tree UX improvements, unify icon library

Streaming tool UI fix (ChatView.tsx):
- Add toolUsesRef/toolResultsRef to reliably track tool data across closures
- Serialize tool_use/tool_result into JSON content-blocks array when building
  assistant message after stream ends, matching backend storage format
- MessageItem.parseToolBlocks() now renders tool UI from history messages
- Clean up refs in finally block and timeout auto-retry path

File tree UX (FileTree.tsx, file-tree.tsx):
- Remove folder path header from right panel, merge search + refresh into one row
- Remove file icon spacer (size-5) so file icons align flush with search box
- Change folder icon color from blue to muted-foreground

Chat list panel (ChatListPanel.tsx):
- Folder header: expanded uses FolderOpenIcon, collapsed uses Folder01Icon
- Add tooltip showing full working directory path on folder hover
- Double-click folder header opens in system file manager

Title bar folder name (chat/[id]/page.tsx):
- Add tooltip with full path on project name hover
- Click opens folder in Finder/Explorer via Electron IPC or API fallback

Open folder support:
- electron/main.ts: add shell:open-path IPC handler via shell.openPath
- electron/preload.ts: expose electronAPI.shell.openPath to renderer
- api/files/open/route.ts: fallback API route using open/explorer/xdg-open

Unify icon library — migrate app-level components from Lucide to Hugeicons:
- file-tree.tsx: folder, file, chevron, plus icons
- tool-actions-group.tsx: chevron expand icon
- MessageItem.tsx: copy, check, expand/collapse icons
- MessageInput.tsx: stop button (SquareIcon → StopIcon)
- FileCard.tsx: file icon
- ImageLightbox.tsx: left/right navigation arrows
- InstallWizard.tsx: status icons (check, x, minus, loader, circle, copy, download)
- Keep Lucide in ui/ and ai-elements/ base layers (shadcn standard)

src/hooks/useSSEStream.ts

@@ -22,6 +22,7 @@ export interface SSECallbacks {
   onResult: (usage: TokenUsage | null) => void;
   onPermissionRequest: (data: PermissionRequestEvent) => void;
   onToolTimeout: (toolName: string, elapsedSeconds: number) => void;
+  onModeChanged: (mode: string) => void;
   onError: (accumulated: string) => void;
 }
 
@@ -129,6 +130,11 @@ function handleSSEEvent(
       return accumulated;
     }
 
+    case 'mode_changed': {
+      callbacks.onModeChanged(event.data);
+      return accumulated;
+    }
+
     case 'error': {
       const next = accumulated + '\n\n**Error:** ' + event.data;
       callbacks.onError(next);
@@ -213,6 +219,7 @@ export function useSSEStream() {
         onResult: (u) => callbacksRef.current?.onResult(u),
         onPermissionRequest: (d) => callbacksRef.current?.onPermissionRequest(d),
         onToolTimeout: (n, s) => callbacksRef.current?.onToolTimeout(n, s),
+        onModeChanged: (m) => callbacksRef.current?.onModeChanged(m),
         onError: (a) => callbacksRef.current?.onError(a),
       };