refactor: remove legacy /shop and /api/v1/shop dead code

After the storefront migration, no live routes mount under /api/v1/shop/.
Remove all dead code that detected/handled shop API requests: the
is_shop_api_request() method, the shop API dispatch branch in middleware,
the RequestContext.SHOP enum member (renamed to STOREFRONT), legacy path
prefixes in FrontendDetector, and all associated tests.

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

.architecture-rules/naming.yaml

@@ -22,7 +22,9 @@ naming_rules:
     description: |
       Service files should use singular name + _service (vendor_service.py)
     pattern:
-      file_pattern: "app/services/**/*.py"
+      file_pattern:
+        - "app/services/**/*.py"
+        - "app/modules/*/services/**/*.py"
       check: "service_naming"
 
   - id: "NAM-003"
@@ -31,14 +33,16 @@ naming_rules:
     description: |
       Both database and schema model files use singular names (product.py)
     pattern:
-      file_pattern: "models/**/*.py"
+      file_pattern:
+        - "models/**/*.py"
+        - "app/modules/*/models/**/*.py"
       check: "singular_naming"
 
   - id: "NAM-004"
     name: "Use consistent terminology: vendor not shop"
     severity: "warning"
     description: |
-      Use 'vendor' consistently, not 'shop' (except for shop frontend)
+      Use 'vendor' consistently, not 'shop' (except for storefront)
     pattern:
       file_pattern: "app/**/*.py"
       discouraged_terms: