feat: comprehensive codebase improvements (cleanup, logic, performance)

Code Cleanups:
- Consolidated PlanTaskStatus and TddPhase types to types.ts
- Standardized node: prefix for Node.js builtin imports
- Fixed timer type to NodeJS.Timeout in respawn-controller

Logic Improvements:
- Fixed AI check race condition with UUID tracking in respawn-controller
- Added comprehensive _isStopped guards in session timer callbacks
- Made RalphTracker reset events non-reentrant via process.nextTick()
- Improved SessionManager mutex pattern reliability

Performance Optimizations:
- Fixed pendingToolCalls memory leak with TTL cleanup in subagent-watcher
- Improved LRUMap.newest() from O(n) to O(1) with _newestKey tracking

Documentation:
- Enhanced README antiflicker section with 6-layer technical details

Version: 0.1441

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

src/session-manager.ts

@@ -100,10 +100,12 @@ export class SessionManager extends EventEmitter {
     }
 
     // Create a new lock promise that others will wait on
-    let unlock: () => void;
-    this._sessionCreationLock = new Promise<void>(resolve => {
+    // Define unlock first to ensure it's always in scope before promise assignment
+    let unlock!: () => void;
+    const lockPromise = new Promise<void>(resolve => {
       unlock = resolve;
     });
+    this._sessionCreationLock = lockPromise;
 
     try {
       const config = this.store.getConfig();
@@ -152,7 +154,7 @@ export class SessionManager extends EventEmitter {
     } finally {
       // Release the lock so other createSession calls can proceed
       this._sessionCreationLock = null;
-      unlock!();
+      unlock();
     }
   }