feat: add a platform-aware apps download page

Serve desktop and Android builds from the latest Gitea release on /download, and fix the desktop compile and CI flakes that blocked v1.3.0.

Co-authored-by: Cursor <cursoragent@cursor.com>

services/api/internal/auth/auth_test.go

@@ -566,5 +566,6 @@ func TestPublicRoutes(t *testing.T) {
 	assert.Equal(t, http.StatusOK, e.do(http.MethodGet, "/api/v1/server-info", nil).Code)
 	assert.Equal(t, http.StatusOK, e.do(http.MethodGet, "/healthz", nil).Code)
 	assert.NotEqual(t, http.StatusUnauthorized, e.do(http.MethodGet, "/api/v1/app/android/latest", nil).Code, "APK page is public")
+	assert.NotEqual(t, http.StatusUnauthorized, e.do(http.MethodGet, "/api/v1/app/clients", nil).Code, "download page is public")
 	assert.Equal(t, http.StatusUnauthorized, e.do(http.MethodGet, "/api/v1/unknown", nil).Code)
 }