Show Nominatim 403 error to user in Web UI

Closes #5

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

matcher/nominatim.py

@@ -31,6 +31,8 @@ def lookup_with_params(**kwargs: str) -> list[Hit]:
     r = requests.get(url, params=params, headers=user_agent_headers())
     if r.status_code == 500:
         raise SearchError
+    if r.status_code == 403:
+        raise SearchError("Nominatim returned 403 Forbidden")
 
     try:
         reply: list[Hit] = json.loads(r.text, object_pairs_hook=OrderedDict)

web_view.py

@@ -653,7 +653,10 @@ def api_missing_wikidata_items():
 @app.route("/api/1/search")
 def api_search():
     q = flask.request.args["q"]
+    try:
         hits = nominatim.lookup(q)
+    except nominatim.SearchError as e:
+        return cors_jsonify({"success": False, "error": str(e)}, 503)
     for hit in hits:
         hit["name"] = nominatim.get_hit_name(hit)
         hit["label"] = nominatim.get_hit_label(hit)