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/marketplace/routes/pages/store.py

@@ -8,11 +8,15 @@ Store pages for marketplace management:
 - Letzshop integration
 """
 
-from fastapi import APIRouter, Depends, Path, Request
+from fastapi import APIRouter, Depends, Request
 from fastapi.responses import HTMLResponse, RedirectResponse
 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.core.utils.page_context import get_store_context
 from app.modules.marketplace.services.onboarding_service import OnboardingService
 from app.modules.service import module_service
@@ -29,11 +33,11 @@ router = APIRouter()
 
 
 @router.get(
-    "/{store_code}/onboarding", response_class=HTMLResponse, include_in_schema=False
+    "/onboarding", response_class=HTMLResponse, include_in_schema=False
 )
 async def store_onboarding_page(
     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),
 ):
@@ -80,11 +84,11 @@ async def store_onboarding_page(
 
 
 @router.get(
-    "/{store_code}/marketplace", response_class=HTMLResponse, include_in_schema=False
+    "/marketplace", response_class=HTMLResponse, include_in_schema=False
 )
 async def store_marketplace_page(
     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),
 ):
@@ -112,11 +116,11 @@ async def store_marketplace_page(
 
 
 @router.get(
-    "/{store_code}/letzshop", response_class=HTMLResponse, include_in_schema=False
+    "/letzshop", response_class=HTMLResponse, include_in_schema=False
 )
 async def store_letzshop_page(
     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),
 ):

app/modules/marketplace/static/store/js/onboarding.js

@@ -615,10 +615,10 @@ function storeOnboarding(initialLang = 'en') {
         async handleLogout() {
             onboardingLog.info('Logging out from onboarding...');
 
-            // Get store code from URL
+            // Get store code from server-rendered value or URL fallback
             const path = window.location.pathname;
             const segments = path.split('/').filter(Boolean);
-            const storeCode = segments[0] === 'store' && segments[1] ? segments[1] : '';
+            const storeCode = window.STORE_CODE || (segments[0] === 'store' && segments[1] ? segments[1] : '');
 
             try {
                 // Call logout API