feat(loyalty): pair POS terminal devices with one-time setup QR

Adds the backend half of the Android tablet rollout. Merchants can
pair tablets to specific stores from /merchants/loyalty/devices (or
admins can pair on behalf from the merchant detail page). Each
pairing issues a long-lived JWT shown ONCE in the response with a
server-rendered QR PNG containing {api_url, store_code, auth_token} —
the tablet scans it on first boot and persists the three fields.

The store API (/api/v1/store/loyalty/*) now accepts these device JWTs
alongside user JWTs. Revoking a device row immediately rejects its
token (401 TERMINAL_DEVICE_REVOKED). Tokens expire after 1 year;
re-pair to renew.

- Migration loyalty_010 + TerminalDevice model
- create_device_token / verify_device_token JWT helpers
- 5 endpoints x 2 portals (merchant + admin on-behalf)
- Bearer-auth wiring in app/api/deps.py
- Pages, shared list partial with one-time pairing-QR modal,
  Alpine.js factories
- Locale strings (en authoritative; fr/de/lb seeded with EN copy
  for translation)
- 6 integration tests covering pair, list, revoke, idempotency,
  cross-merchant rejection, store-API auth via device JWT

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/modules/loyalty/definition.py

@@ -149,6 +149,7 @@ loyalty_module = ModuleDefinition(
             "analytics",  # Merchant loyalty analytics
             "transactions",  # Transaction feed
             "pins",  # Staff PINs
+            "devices",  # Terminal devices (POS tablets)
             "settings",  # Settings (read-only)
         ],
     },
@@ -278,6 +279,13 @@ loyalty_module = ModuleDefinition(
                         route="/merchants/loyalty/pins",
                         order=30,
                     ),
+                    MenuItemDefinition(
+                        id="devices",
+                        label_key="loyalty.menu.terminal_devices",
+                        icon="device-tablet",
+                        route="/merchants/loyalty/devices",
+                        order=32,
+                    ),
                     MenuItemDefinition(
                         id="settings",
                         label_key="loyalty.menu.settings",