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/middleware.md

@@ -14,7 +14,61 @@ This middleware layer is **system-wide** and enables the multi-tenant architectu
 
 ## Middleware Components
 
-### 1. Logging Middleware
+### 1. Platform Context Middleware
+
+**Purpose**: Detect which platform (OMS, Loyalty, Main) the request is for
+
+**What it does**:
+- Detects platform from:
+  - Custom domain (e.g., `oms.lu`, `loyalty.lu`)
+  - Path prefix in development (e.g., `/platforms/oms/`, `/platforms/loyalty/`)
+  - Default to `main` platform for localhost without prefix
+- Rewrites path for platform-prefixed requests (strips `/platforms/{code}/`)
+- Queries database to find platform by domain or code
+- Injects platform object into `request.state.platform`
+
+**URL Detection Logic**:
+```
+Request arrives
+      │
+      ▼
+┌─────────────────────────────────────┐
+│ Production domain? (oms.lu, etc.)   │
+└─────────────────────────────────────┘
+      │ YES → Use that platform
+      │
+      ▼ NO (localhost)
+┌─────────────────────────────────────┐
+│ Path starts with /platforms/{code}? │
+└─────────────────────────────────────┘
+      │ YES → Strip prefix, use platform
+      │       /platforms/oms/pricing → /pricing
+      │
+      ▼ NO
+┌─────────────────────────────────────┐
+│ Use 'main' platform (DEFAULT)       │
+│ Path unchanged                      │
+└─────────────────────────────────────┘
+```
+
+**Example**:
+```
+Request: https://localhost:9999/platforms/oms/pricing
+↓
+Middleware detects: platform_code = "oms"
+↓
+Rewrites path: /platforms/oms/pricing → /pricing
+↓
+Queries database: SELECT * FROM platforms WHERE code = 'oms'
+↓
+Injects: request.state.platform = <Platform object>
+```
+
+**Why it's critical**: Without this, the system wouldn't know which platform's content to serve
+
+**Configuration**: Runs BEFORE VendorContextMiddleware (sets platform context first)
+
+### 2. Logging Middleware
 
 **Purpose**: Request/response logging and performance monitoring
 
@@ -221,13 +275,14 @@ from middleware import context_middleware
 ```mermaid
 graph TD
     A[Client Request] --> B[1. LoggingMiddleware]
-    B --> C[2. VendorContextMiddleware]
-    C --> D[3. ContextDetectionMiddleware]
-    D --> E[4. ThemeContextMiddleware]
-    E --> F[5. FastAPI Router]
-    F --> G[Route Handler]
-    G --> H[Response]
-    H --> I[Client]
+    B --> C[2. PlatformContextMiddleware]
+    C --> D[3. VendorContextMiddleware]
+    D --> E[4. ContextDetectionMiddleware]
+    E --> F[5. ThemeContextMiddleware]
+    F --> G[6. FastAPI Router]
+    G --> H[Route Handler]
+    H --> I[Response]
+    I --> J[Client]
 ```
 
 ### Why This Order Matters
@@ -238,21 +293,27 @@ graph TD
    - Needs to wrap everything to measure total time
    - Must log errors from all other middleware
 
-2. **VendorContextMiddleware second**
+2. **PlatformContextMiddleware second**
+   - Must run before VendorContextMiddleware (sets platform context)
+   - Rewrites path for `/platforms/{code}/` prefixed requests
+   - Sets `request.state.platform` for downstream middleware
+
+3. **VendorContextMiddleware third**
+   - Uses rewritten path from PlatformContextMiddleware
    - Must run before ContextDetectionMiddleware (provides vendor and clean_path)
    - Must run before ThemeContextMiddleware (provides vendor_id)
 
-3. **ContextDetectionMiddleware third**
+4. **ContextDetectionMiddleware fourth**
    - Uses clean_path from VendorContextMiddleware
    - Provides context_type for ThemeContextMiddleware
 
-4. **ThemeContextMiddleware last**
+5. **ThemeContextMiddleware last**
    - Depends on vendor from VendorContextMiddleware
    - Depends on context_type from ContextDetectionMiddleware
 
 **Breaking this order will break the application!**
 
-**Note:** Path-based routing (e.g., `/vendors/{code}/shop/*`) is handled by double router mounting in `main.py`, not by middleware.
+**Note:** Path-based routing (e.g., `/vendors/{code}/shop/*`) is handled by double router mounting in `main.py`, not by middleware. Platform path-based routing (e.g., `/platforms/oms/`) IS handled by PlatformContextMiddleware which rewrites the path.
 
 ## Request State Variables
 
@@ -260,6 +321,8 @@ Middleware components inject these variables into `request.state`:
 
 | Variable | Set By | Type | Used By | Description |
 |----------|--------|------|---------|-------------|
+| `platform` | PlatformContextMiddleware | Platform | Routes, Content | Current platform object (main, oms, loyalty) |
+| `platform_context` | PlatformContextMiddleware | dict | Routes | Platform detection details (method, paths) |
 | `vendor` | VendorContextMiddleware | Vendor | Theme, Templates | Current vendor object |
 | `vendor_id` | VendorContextMiddleware | int | Queries, Theme | Current vendor ID |
 | `clean_path` | VendorContextMiddleware | str | Context | Path without vendor prefix (for context detection) |