fix: replace Pi agent icon with correct logo from shittycodingagent.ai (#3143)

Previous icon was a wrong GitHub avatar (Korean characters). Now uses
the official Pi logo (pixelated P with dot) from the project website.

Co-authored-by: spawn-bot <spawn-bot@openrouter.ai>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-authored-by: Ahmed Abushagur <ahmed@abushagur.com>

assets/agents/.sources.json

@@ -32,7 +32,7 @@
     "ext": "png"
   },
   "pi": {
-    "url": "https://avatars.githubusercontent.com/u/506932?s=200&v=4",
+    "url": "custom:shittycodingagent.ai/logo.svg (official Pi logo, converted to PNG with dark background)",
     "ext": "png"
   }
 }