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/plan-orchestrator.ts

@@ -23,16 +23,14 @@ import {
   RESEARCH_AGENT_PROMPT,
   PLANNER_PROMPT,
 } from './prompts/index.js';
+import { PlanTaskStatus, TddPhase } from './types.js';
 
 // ============================================================================
 // Types
 // ============================================================================
 
-/** Development phase in TDD cycle */
-export type PlanPhase = 'setup' | 'test' | 'impl' | 'verify' | 'review';
-
-/** Task execution status */
-export type PlanTaskStatus = 'pending' | 'in_progress' | 'completed' | 'failed' | 'blocked';
+/** Development phase in TDD cycle (alias for TddPhase) */
+export type PlanPhase = TddPhase;
 
 /**
  * Plan item with TDD structure.
@@ -260,7 +258,9 @@ export class PlanOrchestrator {
     for (const session of this.runningSessions) {
       try {
         session.stop();
-      } catch {}
+      } catch (err) {
+        console.error('[PlanOrchestrator] Failed to stop session during cancel:', err);
+      }
     }
     this.runningSessions.clear();
   }