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/url-routing/overview.md

@@ -37,6 +37,78 @@ http://localhost:8000/vendors/techpro/shop/checkout
 
 ---
 
+## Multi-Platform URL Routing
+
+Wizamart supports multiple platforms (OMS, Loyalty, Site Builder), each with its own marketing site and vendor ecosystem.
+
+### Platform URL Structure
+
+#### Development Mode (localhost)
+
+| URL | What it serves |
+|-----|----------------|
+| `/` | Main marketing site homepage (`main` platform) |
+| `/about` | Main marketing site about page |
+| `/platforms/oms/` | OMS platform homepage |
+| `/platforms/oms/pricing` | OMS platform pricing page |
+| `/platforms/oms/vendors/{code}/` | Vendor storefront on OMS |
+| `/platforms/loyalty/` | Loyalty platform homepage |
+| `/platforms/loyalty/features` | Loyalty platform features page |
+
+#### Production Mode (custom domains)
+
+| URL | What it serves |
+|-----|----------------|
+| `wizamart.lu/` | Main marketing site homepage |
+| `wizamart.lu/about` | Main marketing site about page |
+| `oms.lu/` | OMS platform homepage |
+| `oms.lu/pricing` | OMS platform pricing page |
+| `oms.lu/vendors/{code}/` | Vendor storefront on OMS |
+| `loyalty.lu/` | Loyalty platform homepage |
+
+### Platform Routing Logic
+
+```
+Request arrives
+      │
+      ▼
+┌─────────────────────────────────────┐
+│ Check: Is this production domain?   │
+│ (oms.lu, loyalty.lu, etc.)          │
+└─────────────────────────────────────┘
+      │
+      ├── YES → Route to that platform
+      │
+      ▼ NO (localhost)
+┌─────────────────────────────────────┐
+│ Check: Does path start with         │
+│ /platforms/{code}/ ?                │
+└─────────────────────────────────────┘
+      │
+      ├── YES → Strip prefix, route to platform
+      │         /platforms/oms/pricing → /pricing on OMS
+      │
+      ▼ NO
+┌─────────────────────────────────────┐
+│ Route to MAIN MARKETING SITE        │
+│ (no platform context)               │
+│ /faq → Main site FAQ page           │
+└─────────────────────────────────────┘
+```
+
+### Platform Codes
+
+| Platform | Code | Dev URL | Prod Domain |
+|----------|------|---------|-------------|
+| Main Marketing | `main` | `localhost:9999/` | `wizamart.lu` |
+| OMS | `oms` | `localhost:9999/platforms/oms/` | `oms.lu` |
+| Loyalty | `loyalty` | `localhost:9999/platforms/loyalty/` | `loyalty.lu` |
+| Site Builder | `site-builder` | `localhost:9999/platforms/site-builder/` | `sitebuilder.lu` |
+
+**See:** [Multi-Platform CMS Architecture](../multi-platform-cms.md) for content management details.
+
+---
+
 ## Three Deployment Modes Explained
 
 ### 1. SUBDOMAIN MODE (Production - Recommended)