docs: update routing docs and seed script for production routing changes

Reflect the production routing refactor (ce5b54f): document store dashboard
double-mounting, per-platform subdomain overrides via StorePlatform.custom_subdomain,
get_resolved_store_code dependency, and /merchants/ reserved path. Update seed
script to populate custom_subdomain and StoreDomain.platform_id for demo data.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/architecture/request-flow.md

@@ -82,27 +82,33 @@ logger.info(f"Request: GET /storefront/products from 192.168.1.100")
 - Queries database for store
 - Extracts clean path
 
-**Example Processing** (Subdomain Mode):
+**Example Processing** (Subdomain Mode — Two-Step Lookup):
 
 ```python
 # Input
-host = "orion.platform.com"
+host = "wizatech-rewards.rewardflow.lu"
 path = "/storefront/products"
 
-# Detection logic
-if host != settings.platform_domain:
-    # Subdomain detected
-    store_code = host.split('.')[0]  # "orion"
+# Detection logic — two-step subdomain lookup
+subdomain = host.split('.')[0]  # "wizatech-rewards"
 
-    # Query database
+# Step 1: Check per-platform custom subdomain (StorePlatform.custom_subdomain)
+store_platform = db.query(StorePlatform).filter(
+    StorePlatform.custom_subdomain == subdomain
+).first()
+
+if store_platform:
+    store = store_platform.store
+else:
+    # Step 2: Fall back to standard Store.subdomain
     store = db.query(Store).filter(
-        Store.code == store_code
+        Store.subdomain == subdomain
     ).first()
 
-    # Set request state
-    request.state.store = store
-    request.state.store_id = store.id
-    request.state.clean_path = "/storefront/products"  # Already clean
+# Set request state
+request.state.store = store
+request.state.store_id = store.id
+request.state.clean_path = "/storefront/products"  # Already clean
 ```
 
 **Request State After**:
@@ -116,23 +122,32 @@ request.state.clean_path = "/storefront/products"
 
 **What happens**:
 - FastAPI matches the request path against registered routes
-- For path-based development mode, routes are registered with two prefixes:
-  - `/storefront/*` for subdomain/custom domain
-  - `/stores/{store_code}/storefront/*` for path-based development
+- Both storefront and store dashboard routes are registered with two prefixes each:
+  - Storefront: `/storefront/*` and `/storefront/{store_code}/*`
+  - Store dashboard: `/store/*` and `/store/{store_code}/*`
 
 **Example** (Path-Based Mode):
 
 ```python
-# In main.py - Double router mounting
+# In main.py - Double router mounting for storefront
 app.include_router(storefront_pages.router, prefix="/storefront")
-app.include_router(storefront_pages.router, prefix="/stores/{store_code}/storefront")
+app.include_router(storefront_pages.router, prefix="/storefront/{store_code}")
 
-# Request: /stores/ORION/storefront/products
-# Matches: Second router (/stores/{store_code}/storefront)
-# Route: @router.get("/products")
-# store_code available as path parameter = "ORION"
+# In main.py - Double router mounting for store dashboard
+app.include_router(store_pages.router, prefix="/store")
+app.include_router(store_pages.router, prefix="/store/{store_code}")
+
+# Storefront request: /storefront/ACME/products
+# Matches: Second storefront router (/storefront/{store_code})
+# store_code = "ACME"
+
+# Store dashboard request: /store/ACME/dashboard
+# Matches: Second store router (/store/{store_code})
+# store_code = "ACME"
 ```
 
+Route handlers use the `get_resolved_store_code` dependency to transparently resolve the store code from either the path parameter (dev mode) or middleware state (production subdomain/custom domain).
+
 **Note:** Previous implementations used `PathRewriteMiddleware` to rewrite paths. This has been replaced with FastAPI's native routing via double router mounting.
 
 **Request State After**: No changes to state, but internal path updated