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/tenancy/schemas/auth.py

@@ -249,6 +249,11 @@ class UserContext(BaseModel):
     token_store_code: str | None = None
     token_store_role: str | None = None
 
+    # Set when the request was authenticated by a paired POS terminal device
+    # rather than a human user logging in. The device's row carries the actual
+    # principal for audit; this surfaces it for endpoints that care.
+    terminal_device_id: int | None = None
+
     # Optional profile fields
     first_name: str | None = None
     last_name: str | None = None
@@ -344,4 +349,8 @@ class UserContext(BaseModel):
             data["token_store_code"] = getattr(user, "token_store_code", None)
             data["token_store_role"] = getattr(user, "token_store_role", None)
 
+        # Surface terminal-device principal if the user object came from a
+        # device-token authentication path.
+        data["terminal_device_id"] = getattr(user, "terminal_device_id", None)
+
         return cls(**data)