feat(llm): add LLM integration instructions and handler

* Serve LLM instructions at `/llm`
* Include markdown content for memory instructions
* Update README with LLM integration details
* Add tests for LLM instructions handler
* Modify database migrations to use GUIDs for thoughts and projects

internal/app/app.go

@@ -114,6 +114,7 @@ func routes(logger *slog.Logger, cfg *config.Config, db *store.DB, provider ai.P
 	mcpHandler := mcpserver.New(cfg.MCP, toolSet)
 	mux.Handle(cfg.MCP.Path, auth.Middleware(cfg.Auth, keyring, logger)(mcpHandler))
 	mux.HandleFunc("/favicon.ico", serveFavicon)
+	mux.HandleFunc("/llm", serveLLMInstructions)
 
 	mux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusOK)