fix(devices): keep the existing device name on re-pair and re-login

A dedupe-keyed client re-mint (QR rescan, password/passkey re-login) replaces
the stored record, which also reset the operator-visible name to the app's
hardcoded default ('OpenChamber Mobile'). The app-reported name is now only a
fallback: an explicit pairing label wins, otherwise the replaced record's
label is kept, and the default applies only to a first-ever pairing.

packages/web/server/lib/client-auth/pairing.test.js

@@ -13,7 +13,7 @@ const makeRuntime = async (options = {}) => {
     createClient: vi.fn(async (input) => {
       const client = {
         id: `client-${createdClients.length + 1}`,
-        label: input.label,
+        label: input.label ?? input.fallbackLabel,
         clientKind: input.clientKind,
         authMethod: input.authMethod,
         pairingId: input.pairingId,
@@ -61,6 +61,10 @@ describe('client auth pairing runtime', () => {
       pairingId: created.pairing.id,
       clientKind: 'mobile',
       dedupeKey: 'device-key',
+      // No operator-typed pairing label: the app-reported name is only a
+      // fallback so a re-pair keeps the existing device record's label.
+      label: null,
+      fallbackLabel: 'Iryna iPhone',
     }));
 
     await expect(runtime.redeemPairingSession({