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

llm/instructions.go

@@ -0,0 +1,8 @@
+package llm
+
+import _ "embed"
+
+var (
+	//go:embed memory.md
+	MemoryInstructions []byte
+)