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

migrations/008_update_match_thoughts.sql

@@ -17,13 +17,13 @@ as $$
 begin
   return query
   select
-    t.id,
+    t.guid,
     t.content,
     t.metadata,
     1 - (e.embedding <=> query_embedding) as similarity,
     t.created_at
   from thoughts t
-  join embeddings e on e.thought_id = t.id
+  join embeddings e on e.thought_id = t.guid
   where 1 - (e.embedding <=> query_embedding) > match_threshold
     and t.archived_at is null
     and (embedding_model = '' or e.model = embedding_model)