feat: add auto-clear, timed respawn, and enable on existing sessions

- Add token tracking to Session class (input/output tokens)
- Add auto-clear feature that sends /clear when token threshold reached
- Add API endpoint to enable respawn on existing running sessions
- Add timed duration setting for respawn (auto-stops after N minutes)
- Add TaskTracker class for background task detection and tree display
- Update UI with duration input, auto-clear settings, and "Enable on Current" button
- Add respawn timer display in banner when timed run is active
- Add token count display in respawn banner

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/types.ts

@@ -70,6 +70,10 @@ export interface RespawnConfig {
   interStepDelayMs: number;
   /** Whether to enable respawn loop */
   enabled: boolean;
+  /** Whether to send /clear after update prompt */
+  sendClear: boolean;
+  /** Whether to send /init after /clear */
+  sendInit: boolean;
 }
 
 export interface AppConfig {
@@ -211,6 +215,8 @@ export const DEFAULT_CONFIG: AppConfig = {
     updatePrompt: 'update all the docs and CLAUDE.md',
     interStepDelayMs: 1000,        // 1 second between steps
     enabled: false,                // disabled by default
+    sendClear: true,               // send /clear after update prompt
+    sendInit: true,                // send /init after /clear
   },
 };