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/types/index.ts

@@ -311,6 +311,7 @@ export type SSEEventType =
   | 'result'             // final result with usage stats
   | 'error'              // error occurred
   | 'permission_request' // permission approval needed
+  | 'mode_changed'       // SDK permission mode changed (e.g. plan → code)
   | 'done';              // stream complete
 
 export interface SSEEvent {
@@ -345,6 +346,7 @@ export interface PermissionResponseRequest {
   decision: {
     behavior: 'allow';
     updatedPermissions?: PermissionSuggestion[];
+    updatedInput?: Record<string, unknown>;
   } | {
     behavior: 'deny';
     message?: string;