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/run-summary.ts

@@ -22,6 +22,7 @@ import {
   RunSummaryStats,
   createInitialRunSummaryStats,
 } from './types.js';
+import { CLEANUP_CHECK_INTERVAL_MS } from './config/server-timing.js';
 
 /** Maximum events to keep per session (FIFO trimming) */
 const MAX_EVENTS = 1000;
@@ -36,7 +37,7 @@ const TOKEN_MILESTONE_INTERVAL = 50000;
 const STATE_STUCK_WARNING_MS = 10 * 60 * 1000; // 10 minutes
 
 /** State stuck check interval (ms) */
-const STATE_STUCK_CHECK_INTERVAL = 60 * 1000; // 1 minute
+const STATE_STUCK_CHECK_INTERVAL = CLEANUP_CHECK_INTERVAL_MS;
 
 /**
  * Tracks events and statistics for a session's run summary.