Fix Wikipedia Commons thumbnail URLs: 400px -> 500px (valid size)

- Bumped pithumbsize from 400 to 500 in REST API call
- Changed fallback Commons URL construction to use 500px-
- Rewrote 78 cached image URLs in both caches to 500px

Root cause: Wikipedia Commons restricted /Npx- thumbnail sizes;
only 500px and 1280px are accepted now (400px returns HTTP 400).

src/services/recommender.py

@@ -242,7 +242,7 @@ def _fetch_wiki_image(name: str, city: str = "") -> str:
             if source:
                 return source
             # Article exists but has no thumbnail — try pageimages API instead
-            img_url = f"https://en.wikipedia.org/w/api.php?{urllib.parse.urlencode({'action': 'query', 'titles': title, 'prop': 'pageimages', 'pithumbsize': 400, 'format': 'json'})}"
+            img_url = f"https://en.wikipedia.org/w/api.php?{urllib.parse.urlencode({'action': 'query', 'titles': title, 'prop': 'pageimages', 'pithumbsize': 500, 'format': 'json'})}"
             img_data = _http_get_json(img_url, timeout=10)
             if img_data:
                 pages = img_data.get("query", {}).get("pages", {})
@@ -400,7 +400,7 @@ def _fetch_commons_image(name: str, city: str = "", country: str = "") -> str:
                 filename = title.replace("File:", "").strip()
                 safe = filename.replace(" ", "_")
                 md5 = hashlib.md5(safe.encode()).hexdigest()
-                return f"https://upload.wikimedia.org/wikipedia/commons/thumb/{md5[0]}/{md5[:2]}/{safe}/400px-{safe}"
+                return f"https://upload.wikimedia.org/wikipedia/commons/thumb/{md5[0]}/{md5[:2]}/{safe}/500px-{safe}"
     return ""
 
 
@@ -468,7 +468,7 @@ def _fetch_unsplash_api_image(name: str, city: str = "", country: str = "") -> s
             data = json.loads(resp.read().decode())
         results = data.get("results", [])
         if results:
-            # Use small size (400px wide) — perfect for cards
+            # Use small size (500px wide) — perfect for cards
             return results[0]["urls"]["small"]
     except Exception:
         pass