enrichment: capture failure cause + admin retry button

Each enrichment failure now records {"_error": "...", "_step": "..."} into
enrichment_json, mirrors the message into the errors log (visible in
/logs/protokoll), and the list shows the cause as a tooltip on the
"Fehler beim Abrufen der Infos" text. Admins also get a "erneut versuchen"
link per failed row that re-queues just that flat (POST /actions/enrich-flat).

The pipeline raises a typed EnrichmentError per step (fetch / llm / crash)
so future failure modes don't get swallowed as a silent "failed".

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

web/app.py

@@ -1045,6 +1045,21 @@ async def action_enrich_all(
     return _wohnungen_partial_or_redirect(request, admin)
 
 
+@app.post("/actions/enrich-flat")
+async def action_enrich_flat(
+    request: Request,
+    flat_id: str = Form(...),
+    csrf: str = Form(...),
+    admin=Depends(require_admin),
+):
+    require_csrf(admin["id"], csrf)
+    db.set_flat_enrichment(flat_id, "pending")
+    enrichment.kick(flat_id)
+    db.log_audit(admin["username"], "enrichment.retry",
+                 f"flat={flat_id}", user_id=admin["id"], ip=client_ip(request))
+    return _wohnungen_partial_or_redirect(request, admin)
+
+
 @app.post("/actions/users/delete")
 async def action_users_delete(
     request: Request,