refactor: extract magic numbers to named constants

Low severity code quality improvements:
- session.ts: Add timing constants (SCREEN_STARTUP_DELAY_MS, etc.)
- screen-manager.ts: Add EXEC_TIMEOUT_MS, CR_MAX_ATTEMPTS, etc.
- subagent-watcher.ts: Add display length constants
- server.ts: Add STATS_COLLECTION_INTERVAL_MS, SESSION_LIMIT_WAIT_MS, etc.
- spawn-orchestrator.ts: Add budget ratio constants
- respawn-controller.ts: Use pre-compiled ANSI_ESCAPE_PATTERN
- state-store.ts: Use ES6 import for unlinkSync instead of dynamic require
- app.js: Add notification timing constants

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/respawn-controller.ts

@@ -77,6 +77,9 @@ const PLAN_MODE_OPTION_PATTERN = /\d+\.\s+(Yes|No|Type|Cancel|Skip|Proceed|Appro
 /** Pre-filter: selection indicator arrow for plan mode detection */
 const PLAN_MODE_SELECTOR_PATTERN = /[❯>]\s*\d+\./;
 
+/** Pattern to strip ANSI escape codes from terminal output */
+const ANSI_ESCAPE_PATTERN = /\x1b\[[0-9;]*[A-Za-z]/g;
+
 // Note: The old '↵ send' indicator is no longer reliable in Claude Code 2024+
 // Detection now uses completion message patterns ("for Xm Xs") instead.
 
@@ -1277,7 +1280,8 @@ export class RespawnController extends EventEmitter {
     // This prevents false triggers when Claude pauses briefly mid-work.
     if (this._state === 'confirming_idle' || this._state === 'ai_checking') {
       // Strip ANSI escape codes to check if there's real content
-      const stripped = data.replace(/\x1b\[[0-9;]*[A-Za-z]/g, '').trim();
+      ANSI_ESCAPE_PATTERN.lastIndex = 0;
+      const stripped = data.replace(ANSI_ESCAPE_PATTERN, '').trim();
       if (stripped.length > 2) {
         if (this._state === 'ai_checking') {
           this.log(`Substantial output during AI check ("${stripped.substring(0, 40)}..."), cancelling`);
@@ -1924,7 +1928,8 @@ export class RespawnController extends EventEmitter {
     const tail = buffer.slice(-2000);
 
     // Strip ANSI codes for pattern matching
-    const stripped = tail.replace(/\x1b\[[0-9;]*[A-Za-z]/g, '');
+    ANSI_ESCAPE_PATTERN.lastIndex = 0;
+    const stripped = tail.replace(ANSI_ESCAPE_PATTERN, '');
 
     // Must find numbered option pattern
     if (!PLAN_MODE_OPTION_PATTERN.test(stripped)) return false;