feat: add platform detail/edit admin UI and service enhancements

- Add platform detail and edit admin pages with templates and JS
- Add ContentPageService methods: list_all_platform_pages, list_all_vendor_defaults
- Deprecate /admin/platform-homepage route (redirects to /admin/platforms)
- Add migration to fix content_page nullable columns
- Refine platform and vendor context middleware
- Add platform context middleware unit tests
- Update platforms.js with improved functionality
- Add section-based homepage plan documentation

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

docs/proposals/multi-platform-cms-architecture-implementation-plan.md

@@ -64,14 +64,14 @@ app.add_middleware(VendorContextMiddleware)  # Runs second (existing)
 app.add_middleware(PlatformContextMiddleware)  # Runs first (NEW)
 ```
 
-### 2.3 Update VendorContextMiddleware
+### 2.3 Update VendorContextMiddleware ✅ COMPLETE
 
 File: `middleware/vendor_context.py`
 
-Changes needed:
-- [ ] Use `request.state.platform_clean_path` instead of `request.url.path` for path-based vendor detection
-- [ ] Skip vendor detection if no platform found (platform marketing pages like /oms/pricing)
-- [ ] Pass platform context to vendor lookup for multi-platform vendor support
+Changes completed:
+- [x] Use `request.state.platform_clean_path` instead of `request.url.path` for path-based vendor detection (line 52)
+- [x] Skip vendor detection if no platform found (platform marketing pages like /oms/pricing)
+- [x] Pass platform context to vendor lookup for multi-platform vendor support
 
 ### 2.4 Fix Platform Homepage Route
 
@@ -179,19 +179,19 @@ if settings.environment == "development":
     app.mount("/loyalty", loyalty_router)
 ```
 
-### 5.2 Update Shop Routes
+### 5.2 Update Shop Routes ✅ COMPLETE
 
-- [ ] Add platform context to shop routes
-- [ ] Use `request.state.platform` for template selection
-- [ ] Pass platform to content page lookups
+- [x] Add platform context to shop routes (`shop_pages.py` line 117)
+- [x] Use `request.state.platform` for template selection
+- [x] Pass platform to content page lookups (`platform_id` used in CMS queries)
 
-### 5.3 Test All URL Patterns
+### 5.3 Test All URL Patterns ✅ COMPLETE
 
-Development:
-- [ ] `localhost:9999/oms/` → OMS homepage
-- [ ] `localhost:9999/oms/pricing` → OMS pricing page
-- [ ] `localhost:9999/oms/vendors/{code}/` → Vendor storefront
-- [ ] `localhost:9999/loyalty/` → Loyalty homepage
+Development (using /platforms/ prefix):
+- [x] `localhost:9999/platforms/oms/` → OMS homepage
+- [x] `localhost:9999/platforms/oms/pricing` → OMS pricing page
+- [x] `localhost:9999/platforms/oms/vendors/{code}/` → Vendor storefront
+- [x] `localhost:9999/platforms/loyalty/` → Loyalty homepage
 
 ---