Market View: honest staleness per cell after partial scrapes

- matrix response gains last_scraped per date (max scraped_at across all
  hotels), so column headers show the newest scrape touching the date even
  when the visible hotels were on a failed page
- cells >1h older than the column's latest scrape render italic with *
- every cell tooltip now includes the datestamp the price was scraped

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

backend/api/competitors.py

@@ -520,6 +520,23 @@ async def get_competitor_matrix(
             'scraped_at': row.scraped_at.isoformat() if row.scraped_at else None,
         }
 
+    # Most recent scrape touching each date, across ALL hotels — a partial
+    # scrape may refresh the date without touching the displayed hotels, so
+    # per-cell scraped_at can lag behind this column-level timestamp
+    last_scraped_result = await db.execute(
+        text("""
+            SELECT rate_date, MAX(scraped_at) AS last_scraped
+            FROM booking_com_rates
+            WHERE rate_date >= :from_date AND rate_date <= :to_date
+            GROUP BY rate_date
+        """),
+        {'from_date': start, 'to_date': end}
+    )
+    last_scraped = {
+        row.rate_date.isoformat(): row.last_scraped.isoformat() if row.last_scraped else None
+        for row in last_scraped_result.fetchall()
+    }
+
     # Build date list
     dates = []
     current = start
@@ -532,7 +549,8 @@ async def get_competitor_matrix(
         'to_date': end.isoformat(),
         'dates': dates,
         'hotels': hotels,
-        'rates': rates_by_hotel
+        'rates': rates_by_hotel,
+        'last_scraped': last_scraped
     }