Add Sonner-based notifications and UX polish

tests/media-storage.test.ts

@@ -0,0 +1,14 @@
+import { describe, expect, it } from "vitest";
+
+import { getExtensionForMimeType } from "@/lib/media-storage";
+import { inferMediaKindFromFileName } from "@/lib/media-service";
+
+describe("media upload types", () => {
+  it("accepts gif mime types", () => {
+    expect(getExtensionForMimeType("image/gif")).toBe(".gif");
+  });
+
+  it("treats gif files as images", () => {
+    expect(inferMediaKindFromFileName("animation.gif")).toBe("IMAGE");
+  });
+});