Add stale-scrape health alerting (email + in-app banner)

Silent scraper breakage (200-with-empty-body) went unnoticed for 16 days
because nothing flagged it. Now, after each daily direct scrape, a health
check compares every enabled competitor's freshest captured rate against a
staleness threshold (default 5 days, config: scrape_health_stale_days).

State lives in a new direct_scrape_health table so we alert on transitions
only — one email when a competitor goes stale, one when it recovers, never a
daily repeat. Email uses the stack's shared SMTP integration via
central_settings (recipient: scrape_health_alert_email, else SMTP reply_to/
from) — no new mail secrets in this app. The current stale set also drives an
in-app warning banner on the Direct Rates page (GET /direct/health), with an
on-demand re-check endpoint (POST /direct/health/check).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/api/direct.py

@@ -121,6 +121,31 @@ async def list_hotels(user=Depends(get_current_user)):
         return [dict(r) for r in rows]
 
 
+@router.get("/health")
+async def scrape_health(user=Depends(get_current_user)):
+    """Competitor hotels currently flagged as stale — drives the Direct Rates banner."""
+    require_cap(user, "view_direct_rates")
+    async with AsyncSessionLocal() as db:
+        rows = (await db.execute(text("""
+            SELECT h.id AS hotel_id, h.name,
+                   hh.fresh_as_of, hh.stale_since
+            FROM direct_competitor_hotels h
+            JOIN direct_scrape_health hh ON hh.hotel_id = h.id
+            WHERE hh.state = 'stale' AND h.scrape_enabled = true
+            ORDER BY h.name
+        """))).mappings().all()
+        return {"stale": [dict(r) for r in rows]}
+
+
+@router.post("/health/check")
+async def scrape_health_check(background_tasks: BackgroundTasks, user=Depends(get_current_user)):
+    """Re-evaluate scrape freshness on demand (also runs automatically after each scrape)."""
+    require_cap(user, "manage_hotels")
+    from jobs.check_scrape_health import check_scrape_health
+    background_tasks.add_task(check_scrape_health)
+    return {"status": "checking"}
+
+
 @router.post("/hotels", status_code=201)
 async def create_hotel(body: HotelCreate, user=Depends(get_current_user)):
     require_cap(user, "manage_hotels")