fix: Use ATproto localhost OAuth development mode

- Changed BLUESKY_CLIENT_ID to use http://localhost/ with redirect_uri parameter
- Updated magnitude.config.ts to use localhost:3000 for testing
- Removed public/client-metadata.json (no longer needed with localhost mode)
- Updated OAuth test to expect successful redirect to bsky.social

This leverages ATproto's special localhost client development mode which allows
local OAuth testing without requiring client metadata files.

See: https://atproto.com/specs/oauth#localhost-client-development

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

public/client-metadata.json

@@ -1,14 +0,0 @@
-{
-  "client_id": "http://127.0.0.1:3000/client-metadata.json",
-  "client_name": "Ponderants",
-  "client_uri": "http://127.0.0.1:3000",
-  "redirect_uris": [
-    "http://127.0.0.1:3000/api/auth/callback"
-  ],
-  "scope": "atproto",
-  "grant_types": ["authorization_code", "refresh_token"],
-  "response_types": ["code"],
-  "application_type": "web",
-  "token_endpoint_auth_method": "none",
-  "dpop_bound_access_tokens": true
-}