feat(demo): add kiosk idle-detection and How-to-Play tutorial demo mode

[macan88]

Problem

When AncientBeast runs in kiosk / attract mode with no active players, the screen simply waits with no visual feedback, missing an opportunity to onboard new players and keep the display engaging (issue #2976, related #933).

Solution

Introduces a DemoMode class (src/demo/DemoMode.ts) that:

• Idle detection – arms a 2-minute setTimeout; any pointermove, pointerdown, or keydown event resets the countdown while the game is idle.
• Meaningful-action guard – exposes notifyMeaningfulActivity() so the game board can reset the timer only on real game actions (creature moves, ability use) rather than passive camera pans.
• Cycling tutorial sequence – on timeout, plays the built-in HOW_TO_PLAY_STEPS array (5 slides, 8 s each) via game.onDemoStep() callbacks; easy to extend without touching engine code.
• Instant cancel – attaches a capture-phase listener on demo start so the very first pointerdown or keydown calls game.onDemoCancel() synchronously, guaranteeing no residual game state.
• Kiosk guard – enable() / disable() ensure the demo timer is never armed during a live match.
• Phase 2/3 stubs – DemoSequenceType.AI_BATTLE and HISTORIC_REPLAY are declared and routed through the sequence picker; they return empty step arrays today and will be filled once the state-machine PR merges.

Integration (game.ts)

Add three hook methods to Game:

onDemoStart(seq: DemoSequenceType): void  // show demo overlay
onDemoStep(step: DemoStep, idx: number, total: number): void  // render slide
onDemoCancel(): void  // hide overlay, navigate to main menu

Then in the kiosk entry point:

this.demoMode = new DemoMode(this);
this.demoMode.enable();

And on meaningful board actions:

this.demoMode?.notifyMeaningfulActivity();

Testing

• Added src/demo/DemoMode.test.ts with four focused Jest tests using fake timers:
  1. Demo starts after exactly 2-minute idle
  2. Pointer tap mid-demo cancels instantly and re-arms idle timer
  3. Demo never starts when enable() was not called (non-kiosk guard)
  4. notifyMeaningfulActivity() correctly resets the idle countdown

Closes #2976

[vercel]

@macan88 is attempting to deploy a commit to the FreezingMoon Team on Vercel.

A member of the Team first needs to authorize it.