docs: update documentation for /platforms/ URL routing strategy

- Add multi-platform URL routing section to url-routing/overview.md
- Update multi-platform-cms.md with new request flow diagrams
- Add PlatformContextMiddleware documentation to middleware.md
- Update middleware execution order diagram
- Add Phase 7 (Platform URL Routing Strategy) to implementation plan
- Update platform URL summary tables across all docs

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

docs/architecture/multi-platform-cms.md

@@ -113,13 +113,29 @@ ALTER TABLE content_pages ADD COLUMN is_platform_page BOOLEAN DEFAULT FALSE;
 
 ## Request Flow
 
+### URL Routing Structure
+
+The system uses different URL patterns for development vs production:
+
+**Development (localhost):**
+- Main marketing site: `localhost:9999/` (no prefix) → `main` platform
+- Platform sites: `localhost:9999/platforms/{code}/` → specific platform
+
+**Production (custom domains):**
+- Main marketing site: `wizamart.lu/` → `main` platform
+- Platform sites: `oms.lu/`, `loyalty.lu/` → specific platform
+
+### Request Processing
+
 ```
-Request: GET /oms/vendors/shopname/about
+Request: GET /platforms/oms/vendors/shopname/about
               │
               ▼
 ┌─────────────────────────────────────────────────────────────────────┐
 │ PlatformContextMiddleware                                            │
-│ - Detects platform from path prefix (/oms) or domain                 │
+│ - Detects platform from /platforms/{code}/ prefix or domain          │
+│ - Rewrites path: /platforms/oms/vendors/shopname/about               │
+│                  → /vendors/shopname/about                           │
 │ - Sets request.state.platform = Platform(code='oms')                 │
 │ - Sets request.state.platform_clean_path = /vendors/shopname/about   │
 └─────────────────────────────────────────────────────────────────────┘
@@ -127,7 +143,7 @@ Request: GET /oms/vendors/shopname/about
               ▼
 ┌─────────────────────────────────────────────────────────────────────┐
 │ VendorContextMiddleware                                              │
-│ - Uses platform_clean_path for vendor detection                      │
+│ - Uses rewritten path for vendor detection                           │
 │ - Sets request.state.vendor = Vendor(subdomain='shopname')           │
 └─────────────────────────────────────────────────────────────────────┘
               │
@@ -142,6 +158,30 @@ Request: GET /oms/vendors/shopname/about
 └─────────────────────────────────────────────────────────────────────┘
 ```
 
+### Main Marketing Site (No Platform Prefix)
+
+For requests without the `/platforms/` prefix (e.g., `localhost:9999/about`):
+
+```
+Request: GET /about
+              │
+              ▼
+┌─────────────────────────────────────────────────────────────────────┐
+│ PlatformContextMiddleware                                            │
+│ - No /platforms/ prefix detected                                     │
+│ - Uses DEFAULT_PLATFORM_CODE = 'main'                                │
+│ - Sets request.state.platform = Platform(code='main')                │
+│ - Path unchanged: /about                                             │
+└─────────────────────────────────────────────────────────────────────┘
+              │
+              ▼
+┌─────────────────────────────────────────────────────────────────────┐
+│ Route Handler (platform_pages.py)                                    │
+│ - Gets platform_id from request.state.platform (main)                │
+│ - Loads CMS content for main marketing site                          │
+└─────────────────────────────────────────────────────────────────────┘
+```
+
 ## Admin Interface
 
 ### Platform Management (`/admin/platforms`)
@@ -218,8 +258,8 @@ Request: GET /oms/vendors/shopname/about
 
 1. Insert platform record:
    ```sql
-   INSERT INTO platforms (code, name, description, path_prefix)
-   VALUES ('loyalty', 'Loyalty Program', 'Customer loyalty and rewards', '/loyalty');
+   INSERT INTO platforms (code, name, description, domain, path_prefix)
+   VALUES ('loyalty', 'Loyalty Program', 'Customer loyalty and rewards', 'loyalty.lu', 'loyalty');
    ```
 
 2. Create platform-specific content pages:
@@ -228,8 +268,10 @@ Request: GET /oms/vendors/shopname/about
    VALUES (2, 'home', 'Loyalty Program', '<h1>Welcome</h1>', TRUE);
    ```
 
-3. Configure routing (if using path prefix):
-   - Platform detected by `PlatformContextMiddleware`
+3. Configure routing:
+   - **Development:** Access at `localhost:9999/platforms/loyalty/`
+   - **Production:** Access at `loyalty.lu/`
+   - Platform detected automatically by `PlatformContextMiddleware`
    - No additional route configuration needed
 
 4. Assign vendors to platform:
@@ -237,3 +279,11 @@ Request: GET /oms/vendors/shopname/about
    INSERT INTO vendor_platforms (vendor_id, platform_id)
    VALUES (1, 2);
    ```
+
+### Platform URL Summary
+
+| Platform | Code | Dev URL | Prod URL |
+|----------|------|---------|----------|
+| Main Marketing | `main` | `localhost:9999/` | `wizamart.lu/` |
+| OMS | `oms` | `localhost:9999/platforms/oms/` | `oms.lu/` |
+| Loyalty | `loyalty` | `localhost:9999/platforms/loyalty/` | `loyalty.lu/` |