feat: add shared tutorial framework for game plugins

[Copilot]

Games need a consistent tutorial UX and a shared mechanism to track whether a player has already seen a given tutorial — without duplicating this logic in every plugin.

New: app/components/tutorialService.js

Provides a multi-step modal overlay framework that persists seen-state to the existing progress file under a top-level tutorials key (separate from game scores).

Primary entry point for game plugins:

import { showTutorialIfNeeded } from '../../components/tutorialService.js';

const TUTORIAL_STEPS = [
  { title: 'Welcome', content: '<p>Match the pattern before the timer runs out.</p>' },
  { title: 'Scoring', content: '<p>Each correct match earns <strong>10 points</strong>.</p>' },
];

async function init(gameContainer) {
  // ... bind DOM ...
  await showTutorialIfNeeded('my-game-id', TUTORIAL_STEPS, gameContainer, () => {
    start(); // called immediately if tutorial already seen
  });
}

Full API:

Function	Purpose
showTutorialIfNeeded(gameId, steps, container, onComplete?)	Show overlay only if unseen; call onComplete immediately otherwise
showTutorial(gameId, steps, container, onComplete?)	Always show overlay
hasTutorialBeenSeen(gameId)	Check persisted seen-state
markTutorialSeen(gameId)	Persist seen-state without showing overlay
createTutorialOverlay(steps)	Build modal DOM element (not yet appended)
renderTutorialStep(overlay, steps, stepIndex)	Update overlay for a given step

The overlay is a WCAG AA-compliant role="dialog" modal with Previous/Next navigation, "Got it!" on the last step, and a "Skip Tutorial" link. Focus moves into the panel on open. markTutorialSeen runs in a try/finally so onComplete is always invoked even if IPC persistence fails.

CSS: app/styles/game-shared.css

Adds .tutorial-overlay and all sub-element classes using existing design tokens. No new dependencies.

Docs: .github/copilot-instructions.md

Adds §5d covering stored state shape, step definition, init() integration pattern, full API table, CSS class reference, and testing guidance.

• Fixes Create general framework for game tutorials. #118

[acrosman]

There is at least one function that doesn't have test coverage:
Jest: "global" coverage threshold for functions (100%) not met: 99.84%

Check for other improvements that could be made, and for ways to ensure minimal code bloat from the new code.

[Copilot]

There is at least one function that doesn't have test coverage:
Jest: "global" coverage threshold for functions (100%) not met: 99.84%
...

The uncovered function was the default onComplete = () => {} parameter in showTutorialIfNeeded (line 282). The default was never executed because every test supplied an explicit callback.

Fixed in commits b87aedf and 8c18caf by adding a test that calls showTutorialIfNeeded without onComplete and then clicks "Skip Tutorial", which causes _finish() to invoke the default no-op — bringing function coverage back to 100%.