refactor: codebase cleanup — dead code, regex helper, centralized constants, tests

- Remove unused validateTokenCounts/validateTokensAndCost exports and PlanPhase type alias
- Add execPattern() helper to eliminate 8 repetitive .lastIndex=0 + exec() loops
- Centralize 11 magic number constants into config/ai-defaults.ts and config/server-timing.ts
- Remove stale src/tui from tsconfig.json exclude
- Fix CLAUDE.md inaccuracies (session helpers, app.js line count, module count)
- Add 316 new tests: LRUMap (38), StaleExpirationMap (42), BufferAccumulator (33),
  respawn helpers (142), system-routes expansion (11→61)

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

src/types/plan.ts

@@ -6,7 +6,7 @@
  * Key exports:
  * - PlanItem — a single task with priority (P0/P1/P2), TDD phase, dependencies, verification criteria
  * - PlanTaskStatus — 'pending' | 'in_progress' | 'completed' | 'failed' | 'blocked'
- * - TddPhase / PlanPhase — 'setup' | 'test' | 'impl' | 'verify' | 'review'
+ * - TddPhase — 'setup' | 'test' | 'impl' | 'verify' | 'review'
  *
  * Used by PlanOrchestrator (`src/plan-orchestrator.ts`) and the plan API routes
  * (`src/web/routes/plan-routes.ts`). Served at `GET /api/sessions/:id/plan/tasks`.
@@ -21,9 +21,6 @@ export type PlanTaskStatus = 'pending' | 'in_progress' | 'completed' | 'failed'
 /** TDD phase categories */
 export type TddPhase = 'setup' | 'test' | 'impl' | 'verify' | 'review';
 
-/** Development phase in TDD cycle (alias for TddPhase) */
-export type PlanPhase = TddPhase;
-
 /**
  * A single plan item for plan orchestration.
  * Moved here from plan-orchestrator.ts to break circular dependency.
@@ -42,7 +39,7 @@ export interface PlanItem {
   lastError?: string;
   completedAt?: number;
   complexity?: 'low' | 'medium' | 'high';
-  tddPhase?: PlanPhase;
+  tddPhase?: TddPhase;
   pairedWith?: string;
   reviewChecklist?: string[];
 }