fix(desktop): scope account access to owning client and extend identity verification

Restrict account tracking, probing, and health reporting to accounts owned
by the current client (client_id match). Extend identity-match verification
to bilibili, juejin, and smzdm so session validity is confirmed locally
rather than deferred to remote health state. Server-side account view now
uses stored client_id as authoritative owner instead of presence data.

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

server/internal/tenant/app/desktop_account_service_test.go

@@ -45,7 +45,7 @@ func TestResolveDesktopClientOnline_StaleHeartbeatIsOffline(t *testing.T) {
 	assert.False(t, online)
 }
 
-func TestBuildDesktopAccountView_PrefersAccountPresenceClient(t *testing.T) {
+func TestBuildDesktopAccountView_StoredClientOwnershipWinsOverPresence(t *testing.T) {
 	service := &DesktopAccountService{}
 	accountID := uuid.New()
 	staleClientID := uuid.New()
@@ -75,14 +75,14 @@ func TestBuildDesktopAccountView_PrefersAccountPresenceClient(t *testing.T) {
 	)
 
 	if assert.NotNil(t, view.ClientID) {
-		assert.Equal(t, activeClientID.String(), *view.ClientID)
+		assert.Equal(t, staleClientID.String(), *view.ClientID)
 	}
 	if assert.NotNil(t, view.ClientOnline) {
-		assert.True(t, *view.ClientOnline)
+		assert.False(t, *view.ClientOnline)
 	}
 	assert.Equal(t, "4181862206", view.PlatformUID)
-	assert.Equal(t, &lastSeen, view.ClientLastSeenAt)
-	assert.Equal(t, &deviceName, view.ClientDeviceName)
+	assert.Nil(t, view.ClientLastSeenAt)
+	assert.Nil(t, view.ClientDeviceName)
 }
 
 func TestBuildDesktopAccountView_FallsBackToStoredClientWhenNoPresence(t *testing.T) {