feat: Complete Step 3 & 4 - OAuth + SurrealDB schema

Step 3: ATproto OAuth + SurrealDB JWT
- Implement database-backed OAuth state storage (lib/auth/oauth-state.ts)
- Add session helpers for JWT decoding (lib/auth/session.ts)
- Fix OAuth callback to properly handle state retrieval
- Create /chat page displaying authenticated user handle
- Configure headless mode for Magnitude testing

Step 4: SurrealDB Schema & Permissions
- Define JWT-based access control (HS512 algorithm)
- Create user table with DID-based identity
- Create node table with row-level security (users can only access their own data)
- Create links_to relation table for graph edges
- Define vector search index (1536 dimensions for gemini-embedding-001)
- Add Docker Compose for local SurrealDB development

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

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

magnitude.config.ts

@@ -4,4 +4,6 @@ export default {
   url: 'http://localhost:3000',
   // We will configure magnitude to find tests in this directory
   tests: 'tests/magnitude/**/*.mag.ts',
+  // Run tests in headless mode to avoid window focus issues
+  headless: true,
 };