feat(FN-2394): add Fusion reinstall flow for Pi extensions

- Add dashboard route and server handling to reinstall the Fusion Pi extension
- Introduce a client API helper and wire a reinstall action into PiExtensionsManager
- Polish action spacing and document Fusion reinstall recovery in the CLI README
- Expand route, API, and component tests including reinstall refresh stability coverage
- Add a changeset for @runfusion/fusion patch release

packages/dashboard/app/api.test.ts

@@ -55,6 +55,7 @@ import {
   fetchPiSettings,
   updatePiSettings,
   installPiPackage,
+  reinstallFusionPiPackage,
   fetchPiExtensions,
   updatePiExtensions,
   fetchProjectTasks,
@@ -5962,6 +5963,45 @@ describe("installPiPackage", () => {
   });
 });
 
+describe("reinstallFusionPiPackage", () => {
+  const originalFetch = globalThis.fetch;
+
+  afterEach(() => {
+    globalThis.fetch = originalFetch;
+  });
+
+  it("sends POST to /api/pi-settings/reinstall-fusion", async () => {
+    globalThis.fetch = vi.fn().mockReturnValue(
+      mockFetchResponse(true, { success: true, source: "npm:@runfusion/fusion" })
+    );
+
+    const result = await reinstallFusionPiPackage();
+
+    expect(result).toEqual({ success: true, source: "npm:@runfusion/fusion" });
+    expect(globalThis.fetch).toHaveBeenCalledWith("/api/pi-settings/reinstall-fusion", expect.objectContaining({
+      method: "POST",
+    }));
+  });
+
+  it("forwards projectId query parameter when provided", async () => {
+    globalThis.fetch = vi.fn().mockReturnValue(
+      mockFetchResponse(true, { success: true, source: "npm:@runfusion/fusion" })
+    );
+
+    await reinstallFusionPiPackage("proj-123");
+
+    expect(globalThis.fetch).toHaveBeenCalledWith("/api/pi-settings/reinstall-fusion?projectId=proj-123", expect.objectContaining({
+      method: "POST",
+    }));
+  });
+
+  it("throws API error message on failure", async () => {
+    globalThis.fetch = vi.fn().mockReturnValue(mockFetchResponse(false, { error: "Reinstall failed" }, 500));
+
+    await expect(reinstallFusionPiPackage()).rejects.toThrow("Reinstall failed");
+  });
+});
+
 describe("fetchPiExtensions", () => {
   const originalFetch = globalThis.fetch;