feat(scheduler): in-process matching scheduler with audit + admin endpoints

- Add in-process scheduler service triggered by ENABLE_SCHEDULER
- Record runs in new matching_runs table; throttle per-event and log stats
- Add admin endpoints: POST /api/admin/events/:slug/run-now and GET /api/admin/events/:slug/matching-runs
- Wire scheduler start/stop in server and add ENV flags + compose defaults
- Prisma schema: add MatchingRun model and relation
- Update env examples for scheduler configuration

backend/src/app.js

@@ -117,6 +117,7 @@ app.use('/api/wsdc', require('./routes/wsdc'));
 app.use('/api/divisions', require('./routes/divisions'));
 app.use('/api/competition-types', require('./routes/competitionTypes'));
 app.use('/api/matches', require('./routes/matches'));
+app.use('/api/admin', require('./routes/admin'));
 // app.use('/api/ratings', require('./routes/ratings'));
 
 // 404 handler