feat(ui): PrimaryActionButton gains uploading mode + progress overlay

ui/src/pages/AppsTab/AppDeploymentPage/AppDeploymentPage.module.css

@@ -374,3 +374,29 @@
   background: var(--bg-inset);
   color: var(--text-primary);
 }
+
+/* Primary-button upload progress overlay
+ * Wraps the DS Button so the inner Button can retain its own background
+ * while we overlay a tinted progress fill and label on top. */
+.uploadBtnWrap {
+  display: inline-block;
+}
+
+.uploadBtnWrap button {
+  position: relative;
+  overflow: hidden;
+}
+
+.uploadBtnFill {
+  position: absolute;
+  inset: 0 auto 0 0;
+  background: color-mix(in srgb, var(--primary) 35%, transparent);
+  transition: width 120ms linear;
+  pointer-events: none;
+  z-index: 0;
+}
+
+.uploadBtnLabel {
+  position: relative;
+  z-index: 1;
+}