feat(confidence-engine): define investigation persistence schema

supabase/migrations/20260908000000_create_confidence_engine_investigations.sql

@@ -0,0 +1,53 @@
+create schema if not exists confidence_engine;
+
+create table confidence_engine.investigations (
+  id uuid primary key,
+  user_id uuid not null references auth.users(id) on delete cascade,
+  snapshot jsonb not null,
+  created_at timestamptz not null default now(),
+  updated_at timestamptz not null default now()
+);
+
+create index investigations_user_id_idx
+  on confidence_engine.investigations (user_id);
+
+create function confidence_engine.set_updated_at()
+returns trigger
+language plpgsql
+set search_path = ''
+as $$
+begin
+  new.updated_at = now();
+  return new;
+end;
+$$;
+
+create trigger investigations_set_updated_at
+before update on confidence_engine.investigations
+for each row execute function confidence_engine.set_updated_at();
+
+alter table confidence_engine.investigations enable row level security;
+
+grant usage on schema confidence_engine to authenticated;
+grant select, insert, update, delete on confidence_engine.investigations to authenticated;
+
+create policy "Users can select their own investigations"
+on confidence_engine.investigations
+for select to authenticated
+using (user_id = auth.uid());
+
+create policy "Users can insert their own investigations"
+on confidence_engine.investigations
+for insert to authenticated
+with check (user_id = auth.uid());
+
+create policy "Users can update their own investigations"
+on confidence_engine.investigations
+for update to authenticated
+using (user_id = auth.uid())
+with check (user_id = auth.uid());
+
+create policy "Users can delete their own investigations"
+on confidence_engine.investigations
+for delete to authenticated
+using (user_id = auth.uid());