Rate parity: expected-markup config, alert writer job, alerts UI + direct-link UI

Parity was read-only — the alerts table had no producer, so the Market
View badge could never fire. Now:
- jobs/check_rate_parity.py: daily 06:45 job comparing own Booking.com
  lead-in rate vs cheapest Newbook rate per date, measured against an
  EXPECTED markup (we deliberately price Booking.com higher to cover
  commission): alert when deviation from newbook*(1+markup%) exceeds the
  tolerance. Creates/updates active alerts, auto-resolves dates back in
  line, leaves acknowledged dates alone.
- config keys: parity_check_enabled, parity_expected_markup_pct,
  parity_tolerance_pct (system_config)
- POST /competitors/parity/check manual trigger; GET /parity now uses the
  same markup/tolerance and cheapest-across-categories Newbook rate
- Settings -> Rate Parity tab: markup %, tolerance %, enable toggle,
  run-now with result summary
- Market View -> Parity Alerts tab: status-filtered list w/ acknowledge
- Market View -> Hotels: direct-link dropdown per competitor (new PUT
  /competitors/hotels/{id}/direct-link) — closes the never-written
  direct_hotel_id gap so the matrix direct-rates sub-row can populate

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/scheduler.py

@@ -61,6 +61,13 @@ async def run_scheduled_direct_scrape():
     await loop.run_in_executor(None, run_scrape_all_direct)
 
 
+async def run_scheduled_parity_check():
+    from jobs.check_rate_parity import run_parity_check
+    import asyncio
+    loop = asyncio.get_event_loop()
+    await loop.run_in_executor(None, run_parity_check)
+
+
 async def run_scheduled_booking_scrape_async():
     from jobs.scrape_booking_rates import run_scheduled_booking_scrape
     import asyncio
@@ -116,8 +123,16 @@ def start_scheduler():
         replace_existing=True,
     )
 
+    # Rate parity check — daily at 06:45, after Newbook fetch + Booking scrape
+    scheduler.add_job(
+        run_scheduled_parity_check,
+        CronTrigger(hour=6, minute=45),
+        id='parity_check',
+        replace_existing=True,
+    )
+
     scheduler.start()
-    logger.info(f"Scheduler started: booking scrape at {scrape_hour:02d}:{scrape_minute:02d}, rates fetch at {rates_hour:02d}:{rates_minute:02d}, direct scrape at 06:00")
+    logger.info(f"Scheduler started: booking scrape at {scrape_hour:02d}:{scrape_minute:02d}, rates fetch at {rates_hour:02d}:{rates_minute:02d}, direct scrape at 06:00, parity check at 06:45")
 
 
 def shutdown_scheduler():