Expand AI insight: fix broken competitor query, add continuity, 30-day horizon, holidays

- Fix gather_competitor_data() tier filter: it queried tier IN ('primary','secondary'),
  values that never exist (real values are 'own'/'competitor'/'market'), so the
  cheapest-competitor comparison has always silently returned nothing.
- Feed the previous insight back into the prompt so the model can note what's
  changed/resolved instead of repeating itself.
- Extend forecast horizon from 14 to 30 days; add a per-day revenue table
  alongside the existing occupancy table.
- Annotate the occupancy table with UK (England) bank holidays.
- Add a same-channel market-movement section (B.com vs B.com, rack vs rack)
  diffing rates against the last insight's snapshot, threshold £3.
- Add a parsed headline field + insight history list on the Dashboard,
  collapsed to headline/age and expandable to full content.

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

backend/main.py

@@ -4,6 +4,8 @@ Auth is handled by the central HNF stack cookie (hnf_session).
 """
 import logging
 import sys
+import os
+import time
 from contextlib import asynccontextmanager
 
 logging.basicConfig(
@@ -105,6 +107,9 @@ async def lifespan(app: FastAPI):
                 CREATE INDEX IF NOT EXISTS idx_ai_insights_generated
                 ON ai_insights(generated_at DESC)
             """))
+            db.execute(text("""
+                ALTER TABLE ai_insights ADD COLUMN IF NOT EXISTS headline TEXT
+            """))
             db.commit()
         finally:
             db.close()
@@ -122,6 +127,7 @@ app = FastAPI(
     version="2.0.0",
     lifespan=lifespan,
 )
+STARTED_AT = str(int(time.time() * 1000))
 
 app.add_middleware(
     CORSMiddleware,
@@ -155,4 +161,4 @@ app.include_router(ai_insights.router,       prefix="/ai-insights",       tags=[
 
 @app.get("/health")
 async def health_check():
-    return {"status": "healthy", "service": "forecasting-api"}
+    return {"status": "healthy", "service": "forecasting-api", "version": os.environ.get("BUILD_VERSION", STARTED_AT)}