fix(ui): iOS soft-keyboard shell alignment + hotseat relock on return

iOS Safari/WKWebView does not shrink the layout viewport for the soft
keyboard (Android Chrome does): the visual viewport shrinks AND offsets
down toward the focused field, and the values do not cleanly revert. The
pinned shell tracked only the height (--vvh), not the offset, so its
top-anchored content misaligned on iOS — empty space below the form,
worst on a repeat focus. Fix (one place; covers NewGame, Chat, Feedback):
- app.svelte.ts syncViewport: also mirror visualViewport.offsetTop into
  --vv-top, and scroll the focused field into view on the keyboard-open
  transition (iOS does not reliably scroll a pinned document to it).
- app.css: the pinned app-shell body follows top=--vv-top + height=--vvh
  (was inset:0), so it stays on the visible area.
- e2e/viewport.spec.ts emulates the visual-viewport resize+offset (a fake
  window.visualViewport) to verify the shell follows, on Chromium+WebKit.

Hotseat: returning to the lobby now re-locks the current seat (its PIN is
re-prompted) — LocalSource.relock, cleared in Game.svelte onDestroy.
Root-caused a crash it exposed: a $props() value (id) reads back undefined
during Svelte teardown, so isLocalGameId(id) threw and aborted onDestroy
(breaking navigation) — read the id from the loaded view instead.

ui/e2e/viewport.spec.ts

@@ -0,0 +1,69 @@
+import { test, expect, type Page } from './fixtures';
+
+// Playwright's WebKit has no real soft keyboard, so emulate iOS's visual-viewport behaviour: replace
+// window.visualViewport with a controllable fake BEFORE the app boots. The app's syncViewport
+// (app.svelte.ts) reads visualViewport.height/offsetTop and mirrors them into --vvh / --vv-top, which
+// position the pinned app-shell (app.css html.app-shell body). Driving the fake exercises the exact
+// code path the real keyboard triggers on iOS — where the layout viewport does NOT shrink and the
+// visual viewport instead offsets down toward the focused field.
+async function installFakeViewport(page: Page): Promise<void> {
+  await page.addInitScript(() => {
+    const fake = new EventTarget() as EventTarget & { height: number; offsetTop: number; width: number };
+    fake.height = window.innerHeight;
+    fake.offsetTop = 0;
+    fake.width = window.innerWidth;
+    Object.defineProperty(window, 'visualViewport', { configurable: true, value: fake });
+    (window as unknown as { __vv: typeof fake }).__vv = fake;
+  });
+}
+
+async function setViewport(page: Page, height: number, offsetTop: number): Promise<void> {
+  await page.evaluate(
+    ([h, t]) => {
+      const vv = (window as unknown as { __vv: { height: number; offsetTop: number; dispatchEvent(e: Event): boolean } }).__vv;
+      vv.height = h;
+      vv.offsetTop = t;
+      vv.dispatchEvent(new Event('resize'));
+      vv.dispatchEvent(new Event('scroll'));
+    },
+    [height, offsetTop],
+  );
+}
+
+async function shell(page: Page): Promise<{ vvh: string; top: string; bodyTop: string }> {
+  return page.evaluate(() => ({
+    vvh: getComputedStyle(document.documentElement).getPropertyValue('--vvh').trim(),
+    top: getComputedStyle(document.documentElement).getPropertyValue('--vv-top').trim(),
+    bodyTop: getComputedStyle(document.body).top,
+  }));
+}
+
+test.describe('visual-viewport shell (soft-keyboard alignment)', () => {
+  test('the pinned shell follows the visual viewport height AND offset', async ({ page }) => {
+    await installFakeViewport(page);
+    await page.goto('/');
+    await expect(page.locator('html.app-shell')).toBeAttached();
+    const innerH = await page.evaluate(() => window.innerHeight);
+
+    // Keyboard closed: full height, no offset.
+    await setViewport(page, innerH, 0);
+    let s = await shell(page);
+    expect(s.top).toBe('0px');
+    expect(s.bodyTop).toBe('0px');
+
+    // Keyboard open + iOS offset: the visual viewport shrinks AND offsets down. The pinned shell must
+    // follow BOTH — the body's top must equal the offset (not stay at 0), else the top-anchored
+    // content shows empty space below (the iOS bug this fixes).
+    await setViewport(page, innerH - 300, 180);
+    s = await shell(page);
+    expect(s.vvh).toBe(`${innerH - 300}px`);
+    expect(s.top).toBe('180px');
+    expect(s.bodyTop).toBe('180px');
+
+    // Keyboard closed again: the offset reverts to 0 — no stale shift left behind.
+    await setViewport(page, innerH, 0);
+    s = await shell(page);
+    expect(s.top).toBe('0px');
+    expect(s.bodyTop).toBe('0px');
+  });
+});