Adds FIT file export for activity tracks, alongside the existing GPX export:
- **`FitExporter`** — builds a valid FIT activity (file_id / session / lap / record, plus length / split / set when present) from an `ActivityTrack` + `ActivitySummaryData`.
- **`AutoFitExporter`** + **`AutoExportFitSettingsActivity`** — opt-in auto-export on sync, mirroring the GPX auto-export setting (per-device or all-devices).
- **"Share FIT File"** action in the workout detail menu.
Export is fed device-agnostically: `GarminWorkoutParser` and the shared model (`ActivityTrack` / `ActivityPoint` / `ActivitySummaryEntries` / `ActivityKind`) carry laps, segments, per-length swim, splits/sets, running dynamics and HR zones.
The Garmin FIT codec (`messages`, `baseTypes`, `NativeFITMessage`, `RecordData`) is extended to encode them.
`AutoFitExporter.doExport(...)` is wired beside `AutoGpxExporter` in the Garmin, CMF, Huawei, BangleJS, Huami and Xiaomi activity paths; `FitImporter` also honours the FIT auto-export toggle.
## Testing
`:app:testMainlineDebugUnitTest` — FIT/export subset green:
- `FitExporterReadmeRoundTripTest` — round-trips the curated README sample **and** the full `Activity/<year>/` corpus for years ≥ 2015 from https://github.com/ThomasKuehne/FIT-test-files (3482 files): parse → export → re-parse, asserting GPS/altitude/HR/speed/cadence/distance/power/temp and session aggregates survive.
- `FitExporterPaceTest`, `BaseTypeEncodeRoundTripTest`, `GarminSportTest`, `GPXExporterTest`, `FitImporterTest`, `GpxRouteFileConverterTest`, `FitWeatherTest`.
Thanks a lot to @ThomasKuehne for the initial review
Co-authored-by: Dany Mestas <94061157+DanyPM@users.noreply.github.com>
Reviewed-on: https://codeberg.org/Freeyourgadget/Gadgetbridge/pulls/6268
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persist state via GBDeviceEventUpdatePreferences
added subdivisions as translatable strings
changed start/stop strings to generic ones
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