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/state-store.ts

@@ -14,7 +14,7 @@
  * @module state-store
  */
 
-import { readFileSync, writeFileSync, existsSync, mkdirSync, renameSync } from 'node:fs';
+import { readFileSync, writeFileSync, existsSync, mkdirSync, renameSync, unlinkSync } from 'node:fs';
 import { homedir } from 'node:os';
 import { dirname, join } from 'node:path';
 import { AppState, createInitialState, RalphSessionState, createInitialRalphSessionState, GlobalStats, createInitialGlobalStats, TokenStats, TokenUsageEntry } from './types.js';
@@ -138,7 +138,6 @@ export class StateStore {
       // Try to clean up temp file on error
       try {
         if (existsSync(tempPath)) {
-          const { unlinkSync } = require('node:fs');
           unlinkSync(tempPath);
         }
       } catch { /* ignore cleanup errors */ }
@@ -479,7 +478,6 @@ export class StateStore {
       // Try to clean up temp file on error
       try {
         if (existsSync(tempPath)) {
-          const { unlinkSync } = require('node:fs');
           unlinkSync(tempPath);
         }
       } catch { /* ignore cleanup errors */ }