feat: production routing support for subdomain and custom domain modes

Double-mount store routes at /store/* and /store/{store_code}/* so the
same handlers work in dev path-based, prod path-based, prod subdomain,
and prod custom-domain modes.  Wire StorePlatform.custom_subdomain into
StoreContextMiddleware for per-platform subdomain overrides.  Add admin
custom-domain management UI, fix stale /shop/ reset link, add
/merchants/ to reserved paths, and server-render window.STORE_CODE for
JS that previously parsed the URL.

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

app/modules/cms/routes/pages/store.py

@@ -11,7 +11,11 @@ from fastapi import APIRouter, Depends, HTTPException, Path, Request
 from fastapi.responses import HTMLResponse
 from sqlalchemy.orm import Session
 
-from app.api.deps import get_current_store_from_cookie_or_header, get_db
+from app.api.deps import (
+    get_current_store_from_cookie_or_header,
+    get_db,
+    get_resolved_store_code,
+)
 from app.modules.cms.services import content_page_service
 from app.modules.core.services.platform_settings_service import (
     platform_settings_service,  # MOD-004 - shared platform service
@@ -83,11 +87,11 @@ def get_store_context(
 
 
 @router.get(
-    "/{store_code}/content-pages", response_class=HTMLResponse, include_in_schema=False
+    "/content-pages", response_class=HTMLResponse, include_in_schema=False
 )
 async def store_content_pages_list(
     request: Request,
-    store_code: str = Path(..., description="Store code"),
+    store_code: str = Depends(get_resolved_store_code),
     current_user: User = Depends(get_current_store_from_cookie_or_header),
     db: Session = Depends(get_db),
 ):
@@ -102,13 +106,13 @@ async def store_content_pages_list(
 
 
 @router.get(
-    "/{store_code}/content-pages/create",
+    "/content-pages/create",
     response_class=HTMLResponse,
     include_in_schema=False,
 )
 async def store_content_page_create(
     request: Request,
-    store_code: str = Path(..., description="Store code"),
+    store_code: str = Depends(get_resolved_store_code),
     current_user: User = Depends(get_current_store_from_cookie_or_header),
     db: Session = Depends(get_db),
 ):
@@ -122,13 +126,13 @@ async def store_content_page_create(
 
 
 @router.get(
-    "/{store_code}/content-pages/{page_id}/edit",
+    "/content-pages/{page_id}/edit",
     response_class=HTMLResponse,
     include_in_schema=False,
 )
 async def store_content_page_edit(
     request: Request,
-    store_code: str = Path(..., description="Store code"),
+    store_code: str = Depends(get_resolved_store_code),
     page_id: int = Path(..., description="Content page ID"),
     current_user: User = Depends(get_current_store_from_cookie_or_header),
     db: Session = Depends(get_db),
@@ -148,11 +152,11 @@ async def store_content_page_edit(
 
 
 @router.get(
-    "/{store_code}/{slug}", response_class=HTMLResponse, include_in_schema=False
+    "/{slug}", response_class=HTMLResponse, include_in_schema=False
 )
 async def store_content_page(
     request: Request,
-    store_code: str = Path(..., description="Store code"),
+    store_code: str = Depends(get_resolved_store_code),
     slug: str = Path(..., description="Content page slug"),
     db: Session = Depends(get_db),
 ):