fix: run PM2 cleanup on all platforms for quality migration

Previously skipped Windows PM2 cleanup based on assumption that PM2
wasn't used on Windows. However, this left potential orphaned processes.

Changes:
- Remove platform check (process.platform !== 'win32')
- Run PM2 cleanup on Mac/Linux/Windows consistently
- Create .pm2-migrated marker on all platforms
- Update documentation to reflect cross-platform behavior

Rationale:
- Quality migration should clean up ALL orphaned processes
- Error handling (try/catch) already makes this safe
- Even if PM2 had Windows issues, cleanup won't hurt
- Consistent behavior across platforms is better UX

Impact:
- Windows users will get PM2 cleanup on first hook trigger
- Marker file now created on Windows (prevents repeated attempts)
- No breaking changes (errors caught and ignored)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/shared/worker-utils.ts

@@ -73,7 +73,7 @@ async function startWorker(): Promise<boolean> {
   // Clean up legacy PM2 (one-time migration)
   const pm2MigratedMarker = path.join(SettingsDefaultsManager.get('CLAUDE_MEM_DATA_DIR'), '.pm2-migrated');
 
-  if (process.platform !== 'win32' && !existsSync(pm2MigratedMarker)) {
+  if (!existsSync(pm2MigratedMarker)) {
     try {
       spawnSync('pm2', ['delete', 'claude-mem-worker'], { stdio: 'ignore' });
       // Mark migration as complete