feat(share): a link's address says what it opens

A video stays on /watch/, anything else is given out on /file/ and a folder on /folder/. The token
is the whole key, so every path opens every link and the links already sent keep working. The new
paths are kept out of search indexes like /watch/, boot the player alone, and the unfurl card calls a
file a file.

frontend/src/watch/WatchPage.dom.test.tsx

@@ -24,6 +24,20 @@ afterEach(() => {
   localStorage.clear();
 });
 
+describe("WatchPage share paths", () => {
+  it.each(["/watch/tok-p", "/file/tok-p", "/folder/tok-p", "/file/tok-p/extra"])(
+    "reads the token off %s",
+    async (path) => {
+      window.history.replaceState({}, "", path);
+      mockMeta({ needs_password: false, audio: false, file_url: "/f.mp4", title: "A clip" });
+      render(<WatchPage />);
+      await waitFor(() =>
+        expect(fetch).toHaveBeenCalledWith("/api/public/watch/tok-p", expect.anything()),
+      );
+    },
+  );
+});
+
 describe("WatchPage background play", () => {
   it("hands its <video> to the background-play hook, so Brave iOS keeps it playing", async () => {
     window.history.replaceState({}, "", "/watch/tok-bg");