fix(player): the shut panel keeps the dialog's name; Tab onto a cut link opens the text

With the side panel shut the title heading was gone, and the dialog it named
went unnamed: the strip carries an sr-only copy. A link below a clamp's cut
stayed tabbable out of sight; reaching it now opens the text, measured from the
text's top since focus scrolls the clamped box. DESIGN describes the modal as
built, with log rows for its chrome and the wheel rule.

frontend/src/components/PlayerModal.dom.test.tsx

@@ -629,8 +629,11 @@ describe("PlayerModal — the side panel on a wide window", () => {
     expect(row().style.maxWidth).toBe("calc((100dvh - 3rem - 0px) * 16 / 9 + 2.75rem)");
     // The strip keeps the way out and the stepping.
     expect(within(strip).getByTestId("player-close")).toBeTruthy();
+    // The dialog keeps its name with the title out of sight: it is named by that heading's id.
+    expect(screen.getByRole("dialog", { name: "Video A" })).toBeTruthy();
     fireEvent.click(within(strip).getByRole("button", { name: "player.next" }));
     expect(screen.getByTestId("player-strip")).toBeTruthy(); // still shut on the next video
+    expect(screen.getByRole("dialog", { name: "Video B" })).toBeTruthy();
     fireEvent.click(
       within(screen.getByTestId("player-strip")).getByRole("button", {
         name: "player.expandPanel",