perf: implement phase 1-3 performance optimizations

Add implementation plans and code structure analysis for a 3-phase
performance optimization effort. Refactor core modules to reduce
timer overhead, consolidate regex usage, extract exec timeout config,
add debouncer utility, and streamline server/schema validation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/session-manager.test.ts

@@ -214,6 +214,7 @@ describe('SessionManager', () => {
 
     it('should handle non-existent session gracefully', async () => {
       await expect(manager.stopSession('non-existent')).resolves.not.toThrow();
+      expect(manager.getSessionCount()).toBe(0);
     });
 
     it('should update stored session to stopped', async () => {