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/modules/cms/models/__init__.py

@@ -2,19 +2,20 @@
 """
 CMS module database models.
 
-This package re-exports the ContentPage model from its canonical location
-in models.database. SQLAlchemy models must remain in a single location to
-avoid circular imports at startup time.
+This is the canonical location for CMS models. Module models are automatically
+discovered and registered with SQLAlchemy's Base.metadata at startup.
 
 Usage:
-    from app.modules.cms.models import ContentPage
-
-The canonical model is at: models.database.content_page.ContentPage
+    from app.modules.cms.models import ContentPage, MediaFile, ProductMedia
 """
 
-# Import from canonical location to avoid circular imports
-from models.database.content_page import ContentPage
+from app.modules.cms.models.content_page import ContentPage
+
+# Media models remain in core for now (used by multiple modules)
+from models.database.media import MediaFile, ProductMedia
 
 __all__ = [
     "ContentPage",
+    "MediaFile",
+    "ProductMedia",
 ]