feat: complete CMS as fully autonomous self-contained module

Transform CMS from a thin wrapper into a fully self-contained module with
all code living within app/modules/cms/:

Module Structure:
- models/: ContentPage model (canonical location with dynamic discovery)
- schemas/: Pydantic schemas for API validation
- services/: ContentPageService business logic
- exceptions/: Module-specific exceptions
- routes/api/: REST API endpoints (admin, vendor, shop)
- routes/pages/: HTML page routes (admin, vendor)
- templates/cms/: Jinja2 templates (namespaced)
- static/: JavaScript files (admin/vendor)
- locales/: i18n translations (en, fr, de, lb)

Key Changes:
- Move ContentPage model to module with dynamic model discovery
- Create Pydantic schemas package for request/response validation
- Extract API routes from app/api/v1/*/ to module
- Extract page routes from admin_pages.py/vendor_pages.py to module
- Move static JS files to module with dedicated mount point
- Update templates to use cms_static for module assets
- Add module static file mounting in main.py
- Delete old scattered files (no shims - hard errors on old imports)

This establishes the pattern for migrating other modules to be
fully autonomous and independently deployable.

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

app/api/v1/admin/__init__.py

@@ -48,7 +48,7 @@ from . import (
     background_tasks,
     code_quality,
     companies,
-    content_pages,
+    # content_pages - moved to app.modules.cms.routes.api.admin
     customers,
     dashboard,
     email_templates,
@@ -89,6 +89,9 @@ from app.modules.orders.routes.admin import admin_exceptions_router as orders_ex
 from app.modules.marketplace.routes.admin import admin_router as marketplace_admin_router
 from app.modules.marketplace.routes.admin import admin_letzshop_router as letzshop_admin_router
 
+# CMS module router
+from app.modules.cms.routes.api.admin import router as cms_admin_router
+
 # Create admin router
 router = APIRouter()
 
@@ -117,10 +120,11 @@ router.include_router(vendor_domains.router, tags=["admin-vendor-domains"])
 # Include vendor themes management endpoints
 router.include_router(vendor_themes.router, tags=["admin-vendor-themes"])
 
-# Include content pages management endpoints
+# Include CMS module router (self-contained module)
 router.include_router(
-    content_pages.router, prefix="/content-pages", tags=["admin-content-pages"]
+    cms_admin_router, prefix="/content-pages", tags=["admin-content-pages"]
 )
+# Legacy: content_pages.router moved to app.modules.cms.routes.api.admin
 
 # Include platforms management endpoints (multi-platform CMS)
 router.include_router(platforms.router, tags=["admin-platforms"])