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/002_create_thoughts.sql

@@ -1,10 +1,12 @@
 create table if not exists thoughts (
-  id uuid default gen_random_uuid() primary key,
-  content text not null,
-  embedding vector(1536),
-  metadata jsonb default '{}'::jsonb,
+  id         bigserial   primary key,
+  guid       uuid        not null default gen_random_uuid(),
+  content    text        not null,
+  embedding  vector(1536),
+  metadata   jsonb       default '{}'::jsonb,
   created_at timestamptz default now(),
-  updated_at timestamptz default now()
+  updated_at timestamptz default now(),
+  constraint thoughts_guid_unique unique (guid)
 );
 
 create index if not exists thoughts_embedding_hnsw_idx