revert: restore production to the state before 730d0bd (PM/RBAC work moved to 'pm')

Their three commits (730d0bd, 5a9b543, 387edfb) reached production by push and
auto-deployed. 387edfb expects a users.username column that the live database does
not have, so POST /api/v1/auth/login was returning HTTP 500. Their schema changes
never applied either (projects still has only id, name, description, start_date,
pm_user_id, created_at), so nothing depends on the reverted code.

This commit sets the tree back to exactly a02b3ea — verified with git diff against
it — while keeping history linear: the work itself is preserved on 'pm' at 387edfb.

backend/app/db/init_db.py

@@ -174,7 +174,7 @@ _V26_DDL = [
     """,
     """
     DO $$ BEGIN
-        CREATE TYPE user_role AS ENUM ('pm', 'procurement_manager', 'admin', 'supervisor');
+        CREATE TYPE user_role AS ENUM ('pm', 'procurement_manager', 'admin');
     EXCEPTION WHEN duplicate_object THEN NULL; END $$
     """,
     """