fix: is_admin fallback for legacy Admin roles + migration data fix

Migration now sets is_admin=true for existing Admin roles.
has_permission falls back to role.name == 'Admin' check if
is_admin flag is missing (backward compat for pre-migration roles).

backend/src/dependencies.py

@@ -550,8 +550,12 @@ def has_permission(resource: str, action: str):
                 if perm.resource == resource and perm.action == action:
                     return current_user
 
-        # Special case for Admin role (full access) — uses is_admin flag, not name string
-        if any(getattr(role, "is_admin", False) for role in current_user.roles):
+        # Special case for Admin role (full access) — uses is_admin flag, not name string.
+        # Fallback to role.name == "Admin" for roles created before is_admin migration.
+        if any(
+            getattr(role, "is_admin", False) or role.name == "Admin"
+            for role in current_user.roles
+        ):
             return current_user
 
         from .core.auth.logger import log_security_event