feat(backend): implement dashboard API endpoint

- Add GET /api/dashboard endpoint for authenticated users
- Returns active events with user heats
- Returns accepted matches with partner info
- Detects video exchange status from message parsing
- Tracks rating completion status (rated by me/partner)
- Returns incoming/outgoing pending match requests
- Add comprehensive test suite (12 tests, 93% coverage)
- Add DASHBOARD_PLAN.md with full design documentation

backend/src/app.js

@@ -111,6 +111,7 @@ app.use('/api/', apiLimiter);
 // API routes
 app.use('/api/auth', require('./routes/auth'));
 app.use('/api/users', require('./routes/users'));
+app.use('/api/dashboard', require('./routes/dashboard'));
 app.use('/api/events', require('./routes/events'));
 app.use('/api/wsdc', require('./routes/wsdc'));
 app.use('/api/divisions', require('./routes/divisions'));