fix(sites): Implement BoardGameGeek API detection as suggested

Using the API endpoint suggested by akh7177:
https://api.geekdo.com/api/users?username={}

However, there's an edge case where valid users contain empty arrays
in their JSON response (adminBadges[], userMicrobadges[], supportYears[])
which causes Sherlock's substring matching to incorrectly flag them
as 'not found' when looking for the '[]' error pattern.

The API correctly returns:
- Valid user: JSON object with user data (but contains [] substrings)
- Invalid user: Exactly '[]' (2 characters total)

This needs further refinement to distinguish between the exact '[]'
response vs JSON containing '[]' substrings.

sherlock_project/resources/data.json

@@ -278,6 +278,15 @@
     "urlMain": "https://bsky.app/",
     "username_claimed": "mcuban"
   },
+  "BoardGameGeek": {
+    "errorMsg": "[]",
+    "errorType": "message",
+    "regexCheck": "^[a-zA-Z0-9_]*$",
+    "url": "https://boardgamegeek.com/profile/{}",
+    "urlMain": "https://boardgamegeek.com",
+    "urlProbe": "https://api.geekdo.com/api/users?username={}",
+    "username_claimed": "blue"
+  },
   "BongaCams": {
     "errorType": "status_code",
     "isNSFW": true,