fix: disable terminal UI, fix hydration mismatch

- Remove terminal button from UnifiedTopBar and TerminalDrawer rendering
  Terminal feature disabled until proper node-pty + xterm.js integration
- Fix ChatListPanel hydration mismatch: chatListOpenRaw/chatListWidth
  used window-dependent initializers causing SSR/client divergence
- Improve TerminalInstance for future use: stable useEffect deps,
  ANSI rendering via ansi-to-react, focus management
- Clear CLAUDECODE env var in terminal-manager to allow nested sessions

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

electron/terminal-manager.ts

@@ -51,6 +51,8 @@ export class TerminalManager {
       COLUMNS: String(opts.cols),
       LINES: String(opts.rows),
     };
+    // Allow launching Claude Code inside the terminal
+    delete env.CLAUDECODE;
 
     const child = spawn(shell, shellArgs, {
       cwd: opts.cwd,