Update Timer screen metrics to show C1-C4 duration

[c0d3rb4b4]

Motivation

• Surface a clearer, event-centric metric on the Timer screen by replacing the less-useful Magnitude value with a full-event C1-C4 Duration (elapsed time from first to last contact).
• Use a clearer label for the existing central-path duration by renaming Central Duration to Totality Duration for better user understanding.

Description

• Removed the Magnitude display and added C1-C4 Duration rendering in apps/mobile/src/screens/TimerScreen.tsx.
• Implemented parseUtcTimestamp and formatC1ToC4Duration helpers to compute elapsed time from c1Utc to c4Utc with safe -- fallbacks when timestamps are missing or invalid.
• Renamed the UI label Central Duration to Totality Duration while continuing to display the existing durationSeconds value.
• Bumped mobile package version to 1.1.16 in apps/mobile/package.json and added a 1.1.16 entry to CHANGELOG.md documenting these changes.

Testing

• Ran type checking with pnpm -C apps/mobile typecheck and it completed successfully.
• Ran unit tests with pnpm -C apps/mobile test (Vitest) and all tests passed (5 test files, 16 tests total).

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[chatgpt-codex-connector]

Keep C2-C3 duration label accurate for annular eclipses

durationSeconds is derived from c2→c3 for both total and annular events, so labeling it as Totality Duration is incorrect whenever kindAtLocation === "annular". In those cases the UI reports annularity time with a totality label, which is a user-facing accuracy issue; use a neutral label (e.g., central/phase duration) or switch the label by eclipse type.

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