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/exceptions/content_page.py

@@ -1,43 +0,0 @@
-# app/exceptions/content_page.py
-"""
-DEPRECATED: This module has moved to app.modules.cms.exceptions
-
-Please update your imports:
-    # Old (deprecated):
-    from app.exceptions.content_page import ContentPageNotFoundException
-
-    # New (preferred):
-    from app.modules.cms.exceptions import ContentPageNotFoundException
-
-This shim re-exports from the new location for backwards compatibility.
-"""
-
-import warnings
-
-warnings.warn(
-    "Import from app.modules.cms.exceptions instead of "
-    "app.exceptions.content_page. This shim will be removed in a future version.",
-    DeprecationWarning,
-    stacklevel=2,
-)
-
-# Re-export everything from the new location
-from app.modules.cms.exceptions import (  # noqa: E402, F401
-    ContentPageAlreadyExistsException,
-    ContentPageNotFoundException,
-    ContentPageNotPublishedException,
-    ContentPageSlugReservedException,
-    ContentPageValidationException,
-    UnauthorizedContentPageAccessException,
-    VendorNotAssociatedException,
-)
-
-__all__ = [
-    "ContentPageNotFoundException",
-    "ContentPageAlreadyExistsException",
-    "ContentPageSlugReservedException",
-    "ContentPageNotPublishedException",
-    "UnauthorizedContentPageAccessException",
-    "VendorNotAssociatedException",
-    "ContentPageValidationException",
-]