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/utils/index.ts

@@ -20,8 +20,9 @@ export {
   createAnsiPatternSimple,
   stripAnsi,
   SAFE_PATH_PATTERN,
+  execPattern,
 } from './regex-patterns.js';
-export { MAX_SESSION_TOKENS, validateTokenCounts, validateTokensAndCost } from './token-validation.js';
+export { MAX_SESSION_TOKENS } from './token-validation.js';
 export { stringSimilarity, fuzzyPhraseMatch, todoContentHash } from './string-similarity.js';
 export { assertNever } from './type-safety.js';
 export { wrapWithNice } from './nice-wrapper.js';