feat: Make OAuth configuration environment-aware via NEXT_PUBLIC_APP_URL

- Convert client-metadata.json to dynamic API route reading from env vars
- Remove BLUESKY_CLIENT_ID and BLUESKY_REDIRECT_URI env vars
- All OAuth URLs now derived from NEXT_PUBLIC_APP_URL
- Implement production OAuth client (removes TODO/placeholder)
- Update .prod.env with production settings for www.ponderants.com
- Use https:// for production URLs
- Simplify environment configuration (single source of truth)

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

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

.example.env

@@ -15,10 +15,10 @@ GOOGLE_AI_MODEL=gemini-pro-latest
 # Deepgram API Key (for voice-to-text)
 DEEPGRAM_API_KEY=your-deepgram-api-key
 
-# Bluesky/ATproto OAuth Configuration (localhost development mode)
-# See: https://atproto.com/specs/oauth#localhost-client-development
-BLUESKY_CLIENT_ID=http://localhost/?redirect_uri=http://127.0.0.1:3000/api/auth/callback
-BLUESKY_REDIRECT_URI=http://127.0.0.1:3000/api/auth/callback
+# Application URL (used for OAuth callbacks and client metadata)
+# In development, defaults to http://localhost:3000
+# In production, set to your domain (e.g., https://www.ponderants.com)
+NEXT_PUBLIC_APP_URL=http://localhost:3000
 
 # Test Account Credentials (for E2E tests)
 TEST_BLUESKY_HANDLE=your-test-bluesky-handle