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/003_add_projects.sql

@@ -1,12 +1,14 @@
 create table if not exists projects (
-  id uuid default gen_random_uuid() primary key,
-  name text not null unique,
-  description text,
-  created_at timestamptz default now(),
-  last_active_at timestamptz default now()
+  id             bigserial   primary key,
+  guid           uuid        not null default gen_random_uuid(),
+  name           text        not null unique,
+  description    text,
+  created_at     timestamptz default now(),
+  last_active_at timestamptz default now(),
+  constraint projects_guid_unique unique (guid)
 );
 
-alter table thoughts add column if not exists project_id uuid references projects(id);
+alter table thoughts add column if not exists project_id uuid references projects(guid);
 alter table thoughts add column if not exists archived_at timestamptz;
 
 create index if not exists thoughts_project_id_idx on thoughts (project_id);