feat: improve learning and platform operations

server/migrations/005_audit_log.sql

@@ -0,0 +1,13 @@
+create table audit_logs (
+  id uuid primary key default gen_random_uuid(),
+  actor_id uuid references users(id) on delete set null,
+  action text not null check (char_length(action) between 1 and 120),
+  subject_type text not null check (char_length(subject_type) between 1 and 80),
+  subject_id uuid,
+  metadata jsonb not null default '{}'::jsonb,
+  ip_address inet,
+  created_at timestamptz not null default now()
+);
+
+create index audit_logs_created_index on audit_logs (created_at desc);
+create index audit_logs_actor_index on audit_logs (actor_id, created_at desc);