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/core/routes/pages/store.py

@@ -8,11 +8,15 @@ Store pages for core functionality:
 - Notifications
 """
 
-from fastapi import APIRouter, Depends, Path, Request
+from fastapi import APIRouter, Depends, 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.core.utils.page_context import get_store_context
 from app.modules.tenancy.models import User
 from app.templates_config import templates
@@ -26,11 +30,11 @@ router = APIRouter()
 
 
 @router.get(
-    "/{store_code}/dashboard", response_class=HTMLResponse, include_in_schema=False
+    "/dashboard", response_class=HTMLResponse, include_in_schema=False
 )
 async def store_dashboard_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),
 ):
@@ -55,11 +59,11 @@ async def store_dashboard_page(
 
 
 @router.get(
-    "/{store_code}/media", response_class=HTMLResponse, include_in_schema=False
+    "/media", response_class=HTMLResponse, include_in_schema=False
 )
 async def store_media_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),
 ):
@@ -79,13 +83,13 @@ async def store_media_page(
 
 
 @router.get(
-    "/{store_code}/notifications",
+    "/notifications",
     response_class=HTMLResponse,
     include_in_schema=False,
 )
 async def store_notifications_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/core/static/store/js/init-alpine.js

@@ -74,8 +74,9 @@ function data() {
                 ? segments[segments.length - 2]
                 : last;
 
-            // Get store code from URL
-            if (segments[0] === 'store' && segments[1]) {
+            // Get store code from server-rendered value or URL fallback
+            this.storeCode = window.STORE_CODE || null;
+            if (!this.storeCode && segments[0] === 'store' && segments[1]) {
                 this.storeCode = segments[1];
             }
 
@@ -281,14 +282,18 @@ function emailSettingsWarning() {
         storeCode: null,
 
         async init() {
-            // Get store code from URL
-            const path = window.location.pathname;
-            const segments = path.split('/').filter(Boolean);
-            if (segments[0] === 'store' && segments[1]) {
-                this.storeCode = segments[1];
+            // Get store code from server-rendered value or URL fallback
+            this.storeCode = window.STORE_CODE || null;
+            if (!this.storeCode) {
+                const path = window.location.pathname;
+                const segments = path.split('/').filter(Boolean);
+                if (segments[0] === 'store' && segments[1]) {
+                    this.storeCode = segments[1];
+                }
             }
 
             // Skip if we're on the settings page (to avoid showing banner on config page)
+            const path = window.location.pathname;
             if (path.includes('/settings')) {
                 this.loading = false;
                 return;