Fix preview moon direction: use bearing-based 2D travel vector

[c0d3rb4b4]

Motivation

• The preview moon animation was constrained to a horizontal left/right axis and produced incorrect-looking motion for some locations (notably 2024-like paths); the intent is to compute and apply the true direction between contact bearings so the moon can move diagonally.

Description

• Replaced the 1D travel direction logic with a 2D travel vector: added determinePreviewTravelVector and bearingDegToUnitCirclePoint and applied the vector to both X and Y positioning in calculatePreviewMoonGeometry so the moon path can include vertical drift. (apps/mobile/src/utils/previewGeometry.ts)
• Added describePreviewTravelDirection to produce a short user-facing label for the computed vector and wired it into the preview UI as Moon path: .... (apps/mobile/src/utils/previewGeometry.ts, apps/mobile/src/screens/EclipsePreviewScreen.tsx)
• Updated EclipsePreviewScreen to compute and pass travelVector into the geometry calculation and to display the direction label. (apps/mobile/src/screens/EclipsePreviewScreen.tsx)
• Extended/rewrote tests in apps/mobile/tests/preview-geometry.test.ts to validate diagonal travel vectors, fallback behavior when bearings are missing, and the user-facing direction string. (apps/mobile/tests/preview-geometry.test.ts)
• Bumped the mobile package version to 1.1.12 and added a 1.1.12 entry to CHANGELOG.md. (apps/mobile/package.json, CHANGELOG.md)

Testing

• Ran unit tests with pnpm -C apps/mobile test and all mobile tests passed (5 files, 15 tests passed) including preview-geometry.test.ts (6 tests) which passed.
• Ran targeted test run pnpm -C apps/mobile test -- preview-geometry.test.ts and it passed.
• Ran type checking with pnpm -C apps/mobile typecheck with no errors.
• Ran lint with pnpm -C apps/mobile lint and fixed the reported unused-variable warning; the linter now reports clean.

---

Codex Task