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/config/server-timing.ts

@@ -73,3 +73,16 @@ export const MAX_CONSECUTIVE_ERRORS = 5;
 
 /** Error counter reset interval — forgives errors after quiet period (ms) */
 export const ERROR_RESET_MS = 60_000;
+
+// ============================================================================
+// Common Cleanup Intervals
+// ============================================================================
+
+/** Standard 1-minute cleanup/check interval used by multiple subsystems (ms) */
+export const CLEANUP_CHECK_INTERVAL_MS = 60_000;
+
+/** Standard 1-hour max age for stale/completed data (ms) */
+export const STALE_DATA_MAX_AGE_MS = 60 * 60 * 1000;
+
+/** Standard 5-minute inactivity timeout for streams and caches (ms) */
+export const INACTIVITY_TIMEOUT_MS = 5 * 60 * 1000;