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/task-tracker.ts

@@ -22,6 +22,7 @@
 
 import { EventEmitter } from 'node:events';
 import { assertNever } from './utils/index.js';
+import { STALE_DATA_MAX_AGE_MS } from './config/server-timing.js';
 
 // ========== Configuration Constants ==========
 
@@ -36,7 +37,7 @@ const MAX_COMPLETED_TASKS = 100;
  * Entries older than this are cleaned up to prevent unbounded growth.
  * Default: 1 hour
  */
-const PENDING_TOOL_USE_MAX_AGE_MS = 60 * 60 * 1000;
+const PENDING_TOOL_USE_MAX_AGE_MS = STALE_DATA_MAX_AGE_MS;
 
 /**
  * Maximum number of pending tool uses to allow.