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/definition.py

@@ -9,9 +9,7 @@ This is a self-contained module with:
 - Services: app.modules.cms.services
 - Models: app.modules.cms.models
 - Exceptions: app.modules.cms.exceptions
-
-Templates remain in core (app/templates/admin/) for now due to
-admin/base.html inheritance dependency.
+- Templates: app.modules.cms.templates (namespaced as cms/)
 """
 
 from app.modules.base import ModuleDefinition
@@ -61,8 +59,8 @@ cms_module = ModuleDefinition(
     services_path="app.modules.cms.services",
     models_path="app.modules.cms.models",
     exceptions_path="app.modules.cms.exceptions",
-    # Templates remain in core for now (admin/content-pages*.html)
-    templates_path=None,
+    # Module templates (namespaced as cms/admin/*.html and cms/vendor/*.html)
+    templates_path="templates",
     # Module-specific translations (accessible via cms.* keys)
     locales_path="locales",
 )