Add OTP login flow and multi-cafe role switching

Introduce an OTP input box on login/register, surface user roles and a
cafe chooser, add a dashboard switch button in the POS screen, and
register OTP validators explicitly to survive Docker layer caching.

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

web/dashboard/messages/en.json

@@ -52,7 +52,20 @@
     "noAccount": "Don't have an account?",
     "registerLink": "Register",
     "alreadyRegistered": "This phone is already registered. Please sign in.",
-    "registrationExpired": "Registration session expired. Please try again."
+    "registrationExpired": "Registration session expired. Please try again.",
+    "chooseCafe": "Choose a café",
+    "chooseCafeSubtitle": "This number has access to several cafés. Pick one to continue.",
+    "createNewCafe": "Create a new café",
+    "createNewCafeHint": "Want to start your own café with this number?"
+  },
+  "roles": {
+    "owner": "Owner",
+    "manager": "Manager",
+    "cashier": "Cashier",
+    "waiter": "Waiter",
+    "chef": "Chef",
+    "delivery": "Delivery",
+    "unknown": "User"
   },
   "nav": {
     "aria": "Main navigation",
@@ -93,7 +106,13 @@
     "offline": "Offline",
     "activePlan": "Active plan",
     "editCafeSettings": "Café settings",
-    "viewSubscription": "Plan & billing"
+    "viewSubscription": "Plan & billing",
+    "switchCafe": "Switch café",
+    "currentCafe": "Current café",
+    "otherCafes": "Other cafés",
+    "createNewCafe": "Create a new café",
+    "openMenu": "Menu",
+    "switchCafeError": "Could not switch café. Please try again."
   },
   "overview": {
     "title": "Home",