feat(adminsite): licence delivery, paste instructions and relink

The blob is shown inline as well as offered as a file, because a licence is
signed public data bound to one instance -- useless anywhere else -- and a
blocked download must never leave a paying customer stuck. Admin now returns
it to its owner for the same reason.

Relink shows the remaining allowance from the backend's max_relinks rather
than a hardcoded 3, and at zero it disables and says to contact support
instead of failing at the API.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

adminsite/components/RelinkPanel.test.tsx

@@ -0,0 +1,17 @@
+import { render, screen } from "@testing-library/react";
+import { describe, expect, it, vi } from "vitest";
+import { RelinkPanel } from "./RelinkPanel";
+
+describe("RelinkPanel", () => {
+    it("shows the remaining allowance", () => {
+        render(<RelinkPanel instanceId="i1" used={1} max={3} onRelink={vi.fn()} />);
+        expect(screen.getByText("2 of 3 relinks left this term")).toBeInTheDocument();
+        expect(screen.getByRole("button", { name: /relink/i })).toBeEnabled();
+    });
+
+    it("disables at zero and says what to do instead", () => {
+        render(<RelinkPanel instanceId="i1" used={3} max={3} onRelink={vi.fn()} />);
+        expect(screen.getByRole("button", { name: /relink/i })).toBeDisabled();
+        expect(screen.getByText(/contact support/i)).toBeInTheDocument();
+    });
+});