Fix Timer MAX View moon/sun ratio scaling

[c0d3rb4b4]

Motivation

• The compact MAX View on the Timer hero used a much smaller stage but moon sizes were effectively fixed for the full preview scale, producing wrong proportions in the timer UI.
• The intent is to make the compact (Timer) rendering use the same preview geometry scale so moon/sun ratios and tangency behavior match the full preview.
• Assumed the correct behavior is strict proportional scaling of sun radius and derived moon radii/offsets from the same base preview constants.

Description

• Parameterized moon radius and approach-offset math in apps/mobile/src/utils/previewGeometry.ts so both are computed relative to the supplied sunRadius instead of hard-coded numbers, and added ratio constants for annular/total/partial/none sizing and margins.
• Derived the compact hero sun radius in apps/mobile/src/screens/TimerScreen.tsx from the canonical preview scale using PREVIEW_STAGE_SIZE/PREVIEW_SUN_RADIUS so the Timer MAX View stage uses a proportional sun radius.
• Added regression tests in apps/mobile/tests/preview-geometry.test.ts that verify (1) moon/sun size ratio consistency between full preview and compact stage and (2) preservation of C1/C4 tangency distance in the compact stage.
• Bumped apps/mobile version to 1.1.19 and documented the bugfix in CHANGELOG.md.

Testing

• Ran unit tests: pnpm -C apps/mobile test tests/preview-geometry.test.ts, which executed the preview-geometry suite and resulted in all tests passing (1 file, 9 tests passed).
• Ran typecheck: pnpm -C apps/mobile typecheck, which completed successfully with no TypeScript errors.

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Codex Task