feat(artifacts): storefront layout and Uninstall for installed skills/plugins

- Artifacts page laid out like an app store: hero search, category chips,
  shelves by kind, app-icon cards with one primary pill and a detail sheet
- POST /api/artifacts/:id/uninstall: a skill's copies in ~/.claude/skills and
  ~/.agents/skills are moved to ~/.claude/agenthub-replaced-skills/
  (-uninstalled-<time>), never deleted; a plugin runs
  `claude plugin uninstall --scope user --keep-data` as the caller;
  ENOTINSTALLED when nothing is there; allowed while installs are off
- Uninstall on the card, the ⋯ menu and the detail sheet, after a confirm

client/src/pages/__tests__/Artifacts.test.tsx

@@ -10,8 +10,9 @@
  * server cannot read opens the by-hand form), a skill is uploaded from one
  * Markdown file under the name the user types, or written in the dialog.
  * A card's right-click menu runs the same actions (Preview, Delete). A file
- * the sandbox cannot show (Office, zip, PDF) offers Download only, and the
- * Add menu closes on Escape or a click outside it.
+ * the sandbox cannot show (Office, zip, PDF) offers Download only, the
+ * Add menu closes on Escape or a click outside it, the front page is shelved
+ * by kind until a category is picked, and a card opens its detail sheet.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 import { describe, it, expect, vi, beforeEach } from "vitest";
@@ -32,6 +33,7 @@ vi.mock("../../lib/api", () => ({
       update: vi.fn(),
       remove: vi.fn(),
       install: vi.fn(),
+      uninstall: vi.fn(),
       installs: vi.fn(),
       setInstallsEnabled: vi.fn(),
       skills: vi.fn(),
@@ -294,6 +296,30 @@ describe("Artifacts", () => {
     await waitFor(() => expect(api.artifacts.install).toHaveBeenLastCalledWith(2, true));
   });
 
+  it("uninstalls an installed plugin only after a confirmation", async () => {
+    vi.mocked(api.artifacts.list).mockResolvedValue({
+      items: [
+        item({ id: 4, kind: "plugin", title: "tool", source: "tool@market", installed: true }),
+      ],
+    });
+    vi.mocked(api.artifacts.uninstall).mockReset();
+    open();
+    const card = await screen.findByTestId("artifact-4");
+    const user = userEvent.setup();
+    vi.mocked(confirmDialog).mockResolvedValueOnce(false);
+    await user.click(within(card).getByRole("button", { name: "Uninstall" }));
+    await waitFor(() => expect(confirmDialog).toHaveBeenCalled());
+    expect(api.artifacts.uninstall).not.toHaveBeenCalled();
+
+    vi.mocked(confirmDialog).mockResolvedValueOnce(true);
+    vi.mocked(api.artifacts.uninstall).mockResolvedValueOnce({
+      uninstalled: "tool@market",
+      paths: [],
+    });
+    await user.click(within(card).getByRole("button", { name: "Uninstall" }));
+    await waitFor(() => expect(api.artifacts.uninstall).toHaveBeenCalledWith(4));
+  });
+
   it("installs a skill only after a confirmation, and asks before replacing", async () => {
     const user = userEvent.setup();
     open();
@@ -315,8 +341,8 @@ describe("Artifacts", () => {
   it("previews a file in a sandboxed iframe that may run nothing", async () => {
     const user = userEvent.setup();
     open();
-    await screen.findByText("report.html");
-    await user.click(screen.getAllByRole("button", { name: "Preview" })[0]!);
+    const card = await screen.findByTestId("artifact-1");
+    await user.click(within(card).getByRole("button", { name: "Preview" }));
     const frame = await screen.findByTestId("artifact-preview");
     expect(frame.getAttribute("sandbox")).toBe("");
     expect(frame.getAttribute("src")).toBe("/api/artifacts/1/raw?path=report.html");
@@ -425,4 +451,22 @@ describe("Artifacts", () => {
     await user.click(screen.getByText("report.html"));
     expect(screen.queryByRole("button", { name: "Skill" })).toBeNull();
   });
+
+  it("shelves the front page by kind, and a card opens its detail sheet", async () => {
+    const user = userEvent.setup();
+    open();
+    await screen.findByText("deploy");
+    const shelves = screen.getAllByRole("heading", { level: 2 }).map((h) => h.textContent);
+    expect(shelves).toEqual(["Skills1", "Files1"]);
+    await user.click(screen.getAllByRole("button", { name: "See all" })[0]!);
+    await waitFor(() =>
+      expect(api.artifacts.list).toHaveBeenLastCalledWith(
+        expect.objectContaining({ kind: "skill" })
+      )
+    );
+    await user.click(screen.getByText("deploy"));
+    const sheet = await screen.findByTestId("artifact-detail");
+    expect(within(sheet).getByText("/deploy")).toBeInTheDocument();
+    expect(within(sheet).getByRole("button", { name: "Install" })).toBeInTheDocument();
+  });
 });