fix: resolve circular import in module system

The circular import occurred because:
1. app.modules.base imported FrontendType from models.database.admin_menu_config
2. This triggered models/database/__init__.py which runs model discovery
3. Model discovery imported module definitions
4. Module definitions imported from app.modules.base (still initializing)

Solution: Move FrontendType and MANDATORY_MENU_ITEMS to a new
app/modules/enums.py file. The models file re-exports them for
backward compatibility with existing imports.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

models/database/admin_menu_config.py

@@ -19,8 +19,6 @@ Design:
 - Only stores non-default state (is_visible=False) to keep table small
 """
 
-import enum
-
 from sqlalchemy import (
     Boolean,
     CheckConstraint,
@@ -37,30 +35,11 @@ from sqlalchemy.orm import relationship
 from app.core.database import Base
 from models.database.base import TimestampMixin
 
-
-class FrontendType(str, enum.Enum):
-    """Frontend types that can have menu configuration."""
-
-    ADMIN = "admin"    # Admin panel (super admins, platform admins)
-    VENDOR = "vendor"  # Vendor dashboard
-
-
-# Menu items that cannot be hidden - always visible regardless of config
-# Organized by frontend type
-MANDATORY_MENU_ITEMS = {
-    FrontendType.ADMIN: frozenset({
-        "dashboard",  # Default landing page after login
-        "companies",
-        "vendors",
-        "admin-users",
-        "settings",
-        "my-menu",  # Super admin menu config - must always be accessible
-    }),
-    FrontendType.VENDOR: frozenset({
-        "dashboard",  # Default landing page after login
-        "settings",
-    }),
-}
+# Import FrontendType and MANDATORY_MENU_ITEMS from the central location
+# and re-export for backward compatibility with existing imports.
+# These were moved to app.modules.enums to break a circular import:
+# app.modules.base -> models.database -> model discovery -> module definitions -> app.modules.base
+from app.modules.enums import FrontendType, MANDATORY_MENU_ITEMS
 
 
 class AdminMenuConfig(Base, TimestampMixin):