wohnungen: preserve map across HTMX polls, add rejected section, drop €/m²

- #flats-map uses hx-preserve; marker data moved to <script type="application/json">
  sibling that diffs+updates instead of rebuilding Leaflet every poll (fixes
  whitescreen + tiles rendering outside the card)
- upsert_flat backfills lat/lng on existing rows missing coords (older flats
  scraped before the lat/lng migration now appear on the map once alert re-submits)
- collapsible "Abgelehnte Wohnungen" section at the bottom with Wiederherstellen
- remove €/m² column from the list

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/db.py

@@ -395,8 +395,17 @@ def update_preferences(user_id: int, data: dict) -> None:
 def upsert_flat(payload: dict) -> bool:
     flat_id = str(payload["id"])
     with _lock:
-        existing = _conn.execute("SELECT id FROM flats WHERE id = ?", (flat_id,)).fetchone()
+        existing = _conn.execute(
+            "SELECT id, lat, lng FROM flats WHERE id = ?", (flat_id,)
+        ).fetchone()
         if existing:
+            # Backfill coords on old rows that pre-date the lat/lng migration.
+            if (existing["lat"] is None or existing["lng"] is None) \
+                    and payload.get("lat") is not None and payload.get("lng") is not None:
+                _conn.execute(
+                    "UPDATE flats SET lat = ?, lng = ? WHERE id = ?",
+                    (payload["lat"], payload["lng"], flat_id),
+                )
             return False
         c = payload.get("connectivity") or {}
         _conn.execute(
@@ -508,6 +517,16 @@ def rejected_flat_ids(user_id: int) -> set[str]:
     return {row["flat_id"] for row in rows}
 
 
+def rejected_flats(user_id: int, limit: int = 200) -> list[sqlite3.Row]:
+    return list(_conn.execute(
+        """SELECT f.*, r.rejected_at
+             FROM flat_rejections r JOIN flats f ON f.id = r.flat_id
+            WHERE r.user_id = ?
+            ORDER BY r.rejected_at DESC LIMIT ?""",
+        (user_id, limit),
+    ).fetchall())
+
+
 def last_application_for_flat(user_id: int, flat_id: str) -> Optional[sqlite3.Row]:
     return _conn.execute(
         """SELECT * FROM applications