Add Time Tracking backend API

Implementovaný kompletný backend pre time tracking:
- Nová tabuľka time_entries s foreign keys na users, projects, todos, companies
- Service layer s business logikou pre CRUD operácie
- Controller pre všetky endpointy
- Validačné schémy pomocou Zod
- Routes s autentifikáciou a validáciou
- Endpointy:
  * POST /api/time-tracking/start - Spustenie timeru
  * POST /api/time-tracking/:id/stop - Zastavenie timeru
  * GET /api/time-tracking/running - Získanie bežiaceho záznamu
  * GET /api/time-tracking/month/:year/:month - Mesačné záznamy
  * GET /api/time-tracking/stats/monthly/:year/:month - Mesačné štatistiky
  * PATCH /api/time-tracking/:id - Aktualizácia záznamu
  * DELETE /api/time-tracking/:id - Zmazanie záznamu
- Podpora pre isEdited flag pri editácii
- Kalkulácia duration v minútach

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

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

src/app.js

@@ -22,6 +22,7 @@ import companyRoutes from './routes/company.routes.js';
 import projectRoutes from './routes/project.routes.js';
 import todoRoutes from './routes/todo.routes.js';
 import noteRoutes from './routes/note.routes.js';
+import timeTrackingRoutes from './routes/time-tracking.routes.js';
 
 const app = express();
 
@@ -82,6 +83,7 @@ app.use('/api/companies', companyRoutes);
 app.use('/api/projects', projectRoutes);
 app.use('/api/todos', todoRoutes);
 app.use('/api/notes', noteRoutes);
+app.use('/api/time-tracking', timeTrackingRoutes);
 
 // Basic route
 app.get('/', (req, res) => {