feat: multi-module improvements across merchant, store, i18n, and customer systems

- Fix platform-grouped merchant sidebar menu with core items at root level
- Add merchant store management (detail page, create store, team page)
- Fix store settings 500 error by removing dead stripe/API tab
- Move onboarding translations to module-owned locale files
- Fix onboarding banner i18n with server-side rendering + context inheritance
- Refactor login language selectors to use languageSelector() function (LANG-002)
- Move HTTPException handling to global exception handler in merchant routes (API-003)
- Add language selector to all login pages and portal headers
- Fix customer module: drop order stats from customer model, add to orders module
- Fix admin menu config visibility for super admin platform context
- Fix storefront auth and layout issues
- Add missing i18n translations for onboarding steps (en/fr/de/lb)

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

static/locales/en.json

@@ -111,7 +111,35 @@
     "invalid_credentials": "Invalid username or password",
     "session_expired": "Your session has expired. Please login again.",
     "account_locked": "Your account has been locked",
-    "account_inactive": "Your account is inactive"
+    "account_inactive": "Your account is inactive",
+    "signing_in": "Signing in...",
+    "sending": "Sending...",
+    "send_reset_link": "Send Reset Link",
+    "reset_password_desc": "Enter your email address and we'll send you a link to reset your password.",
+    "back_to_login": "Back to Login",
+    "back_to_platform": "Back to Platform",
+    "no_account": "Don't have an account?",
+    "visit_platform": "Visit our platform",
+    "already_have_account": "Already have an account?",
+    "create_account": "Create an account",
+    "continue_shopping": "Continue shopping",
+    "admin_login": "Admin Login",
+    "merchant_login": "Merchant Login",
+    "store_login": "Store Portal Login",
+    "customer_login": "Customer Login",
+    "create_account_title": "Create Account",
+    "creating_account": "Creating account...",
+    "sign_in_instead": "Sign in instead",
+    "first_name": "First Name",
+    "last_name": "Last Name",
+    "phone_number": "Phone Number",
+    "marketing_consent": "I'd like to receive news and special offers",
+    "password_requirements": "Must contain at least 8 characters, one letter, and one number",
+    "check_email": "Check Your Email",
+    "reset_link_sent": "We've sent a password reset link to your email. Please check your inbox and click the link to reset your password.",
+    "didnt_receive_email": "Didn't receive the email? Check your spam folder or",
+    "try_again": "try again",
+    "remember_password": "Remember your password?"
   },
   "nav": {
     "dashboard": "Dashboard",
@@ -195,5 +223,11 @@
   "clipboard": {
     "copied": "Copied to clipboard",
     "failed": "Failed to copy"
+  },
+  "onboarding": {
+    "banner": {
+      "title": "Get Started",
+      "dismiss": "Dismiss"
+    }
   }
 }