test(harness): the help overlay follows the app to /app/ (#47)

The merge of `gh/main` was clean and that is the hazard: #47 moved the app
from the site root to `/app/` and rewrote all six `goto` calls, while my help
test — added on a branch that did not exist when #47 was written — still
navigated to `/index.html`, which is now the landing page. Git had no reason
to call that a conflict.

Also folds in a cosmetic fix held back from the previous push: `step` had two
`── panels ──` section headers after `cycle-panel-focus` landed in its own
block. One block now.

Verified on the merged tree: 1324 tests, clippy, fmt, both comment-run modes,
wasm for all eight gated crates, and 7/7 Chromium shell tests against the
assembled site.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

harness/tests/shell.spec.js

@@ -133,7 +133,7 @@ test.describe("the help overlay", () => {
   // improvise-ktv1. `?` has entered AppMode::Help in the browser since the
   // keymap was shared; what was missing was anything to draw.
   test("? opens help, and its rows are the shared ones", async ({ page }) => {
-    await page.goto("/index.html");
+    await page.goto("/app/index.html");
     await expect(page.locator("#grid table")).toBeVisible({ timeout: 20_000 });
     await expect(page.locator("#help")).toBeHidden();