feat(data-safety): scheduled DB backups + audit trail + verified actor attribution

- db-backup sidecar: pg_dump -Fc of procurement+casdoor every
  BACKUP_INTERVAL_SECONDS into BACKUP_DIR, retention via BACKUP_KEEP_DAYS
- audit_log table (migration.sql + runtime ensure_audit_table) with
  model + transactional helper (utils/audit.record) — wired into user
  create/role-change and inventory transaction creation
- get_actor: quote_events.actor now stores the VERIFIED user's display
  name instead of the raw bearer token

backend/app/routers/users.py

@@ -21,6 +21,7 @@ from sqlalchemy import select, update
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.auth import UserContext, get_current_user, require_role
+from app.utils.audit import record as audit_record
 from app.config import settings
 from app.db.engine import get_db
 from app.models.procurement import Project, User
@@ -168,7 +169,7 @@ async def list_users(
 @router.post("", status_code=201)
 async def create_user(
     payload: UserCreate,
-    _: UserContext = Depends(_org_manager),
+    ctx: UserContext = Depends(_org_manager),
     db: AsyncSession = Depends(get_db),
 ):
     """Define a new user (manual identity — casdoor_id optional)."""
@@ -185,6 +186,7 @@ async def create_user(
     )
     db.add(user)
     await db.flush()
+    await audit_record(db, actor=ctx.display_name, action="user.created", entity="user", entity_id=str(user.id), details={"role": payload.role})
     return {"data": user_to_dict(user)}
 
 
@@ -192,7 +194,7 @@ async def create_user(
 async def update_user_role(
     user_id,
     payload: UserRoleUpdate,
-    _: UserContext = Depends(require_role("admin")),
+    ctx: UserContext = Depends(require_role("admin")),
     db: AsyncSession = Depends(get_db),
 ):
     """Set/clear a role — ADMIN ONLY (RBAC): procurement managers must not
@@ -201,10 +203,12 @@ async def update_user_role(
     user = await db.get(User, user_id)
     if user is None:
         raise NotFoundError("کاربر یافت نشد")
+    previous_role = user.role
     if user.role == "pm" and payload.role != "pm":
         await _unassign_projects(db, user.id)
     user.role = payload.role
     await db.flush()
+    await audit_record(db, actor=ctx.display_name, action="user.role_changed", entity="user", entity_id=str(user.id), details={"from": previous_role, "to": payload.role})
     projects = await _user_projects(db, user)
     return {"data": user_to_dict(user, projects)}