feat: <gm-shell> wiring, styles, and AFTERIMAGE boot

Adds the gm-shell root element that owns store/clock/stamps/scenario,
mounts director-rail and dice-tray, handles reached (stamp + persist)
and open-tool (toggle dice tray), and boots the AFTERIMAGE scenario in
main.js. Also adds tests/setup.js + a vite.config.js setupFiles entry:
Node's newer built-in global `localStorage` shadows jsdom's per-window
implementation in vitest's jsdom environment, leaving localStorage
undefined in tests until replaced with a real jsdom-backed instance.

tests/components/gm-shell.test.js

@@ -0,0 +1,38 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import '../../src/components/gm-shell.js';
+import afterimage from '../../src/scenarios/afterimage.js';
+
+describe('<gm-shell>', () => {
+  let el, t;
+  beforeEach(() => {
+    localStorage.clear();
+    document.body.innerHTML = '';
+    t = 0;
+    el = document.createElement('gm-shell');
+    el.now = () => t;
+    document.body.appendChild(el);
+    el.loadScenario(afterimage);
+  });
+
+  it('mounts a director-rail for the loaded scenario', () => {
+    expect(el.querySelector('director-rail')).not.toBe(null);
+    expect(el.querySelector('director-rail [data-role=here]').textContent).toContain('The pier');
+  });
+
+  it('stamps the next beat on "reached" and persists it', () => {
+    el.startSession();          // start at t=0
+    t = 6 * 60000;              // 6 minutes later
+    el.querySelector('[data-role=reached]').dispatchEvent(new CustomEvent('reached', { bubbles: true }));
+    expect(el.stamps['a1-open']).toBeCloseTo(6, 5);
+    const persisted = JSON.parse(localStorage.getItem('gmd.afterimage.stamps'));
+    expect(persisted['a1-open']).toBeCloseTo(6, 5);
+    // rail now shows the reached beat as current
+    expect(el.querySelector('director-rail [data-role=here]').textContent).toContain('The pier');
+  });
+
+  it('reveals the dice tray on open-tool', () => {
+    expect(el.querySelector('dice-tray').hidden).toBe(true);
+    el.dispatchEvent(new CustomEvent('open-tool', { detail: { tool: 'dice' }, bubbles: true }));
+    expect(el.querySelector('dice-tray').hidden).toBe(false);
+  });
+});

tests/setup.js

@@ -0,0 +1,14 @@
+// Workaround: Node's own experimental global `localStorage` (added in recent
+// Node versions) shadows jsdom's per-window localStorage before vitest's
+// jsdom environment can install it, leaving `localStorage`/`window.localStorage`
+// undefined in tests. Replace it with a real jsdom-backed Storage instance.
+import { JSDOM } from 'jsdom';
+
+if (typeof localStorage === 'undefined' || typeof localStorage.setItem !== 'function') {
+  const { window } = new JSDOM('', { url: 'http://localhost/' });
+  Object.defineProperty(globalThis, 'localStorage', {
+    value: window.localStorage,
+    configurable: true,
+    writable: true,
+  });
+}