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/regex-patterns.ts

@@ -79,3 +79,15 @@ export function stripAnsi(text: string): string {
 export const SPINNER_PATTERN = /[⠋⠙⠹⠸⠼⠴⠦⠧]/;
 
 export const SAFE_PATH_PATTERN = /^[a-zA-Z0-9_/\-. ~]+$/;
+
+/**
+ * Execute a global regex pattern against data, calling the callback for each match.
+ * Automatically resets lastIndex before execution.
+ */
+export function execPattern(pattern: RegExp, data: string, callback: (match: RegExpExecArray) => void): void {
+  pattern.lastIndex = 0;
+  let match: RegExpExecArray | null;
+  while ((match = pattern.exec(data)) !== null) {
+    callback(match);
+  }
+}