The battery pass: paint less, wake less

- opaque canvas: the compositor stops alpha-blending 2.5Mpx at 60Hz
- settled modals and the death summary idle at 20-24 fps; play untouched
- TUNE.lowPower caps RES at 3 (-44% pixels/frame), flippable live

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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