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/transcript-watcher.ts

@@ -10,10 +10,10 @@
  * The transcript path is provided by Claude Code hooks in the `transcript_path` field.
  */
 
-import { EventEmitter } from 'events';
-import { watch, statSync, existsSync, FSWatcher } from 'fs';
-import { createReadStream } from 'fs';
-import { createInterface } from 'readline';
+import { EventEmitter } from 'node:events';
+import { watch, statSync, existsSync, FSWatcher } from 'node:fs';
+import { createReadStream } from 'node:fs';
+import { createInterface } from 'node:readline';
 
 // ========== Types ==========