Add zoom steps and a larger start caption to the game link (#266)

The released game only ever zoomed in whole steps up to 400%, so a
small camera on a large screen stayed far smaller than it could be.
The "Click to play" caption was drawn in the 11 px panel title size
and was easy to miss.

- GAME_SCALE_STEPS gains 300%, 500% and 600%. The game tab picker,
  Auto in the editor and the game link all read the same list.
- The start caption takes its size from the new Theme.captionSize
  (16) instead of a constant in GameScreen.
- The player page keeps the default arrow cursor at all times. It no
  longer switches to the hand over the caption.

Tests:
- view.test: Auto for 320x180 in 2000x2000 is now 6, with cases
  for 3 and 5. play-settings.test takes 2.5 and 8 as invalid steps.
- e2e 60 checks the caption against the panel title size and the
  arrow cursor before and after the start. Module 03 follows the new
  step list.
- ./check.sh 2808 tests, CHECK EXIT 0 (before the last Theme tweak,
  which changes no test). Full e2e run ALL PASSED, 1574 checks.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/editor/play-settings.test.ts

@@ -40,7 +40,10 @@ describe('play settings in the project', () => {
     expect(playFromOf(null)).toBe('start');
     expect(gameScaleOf({ gameScale: 'fit' })).toBe('fit');
     expect(gameScaleOf({ gameScale: 0.25 })).toBe(0.25);
-    expect(gameScaleOf({ gameScale: 3 })).toBe(1);
+    expect(gameScaleOf({ gameScale: 3 })).toBe(3);
+    expect(gameScaleOf({ gameScale: 6 })).toBe(6);
+    expect(gameScaleOf({ gameScale: 2.5 })).toBe(1);
+    expect(gameScaleOf({ gameScale: 8 })).toBe(1);
     expect(gameScaleOf({ gameScale: '2' })).toBe(1);
   });