Migrate off deprecated PositionConfig.gps_enabled (use gps_mode)

[garthvh]

🤖 Good task for an agent: this is a self-contained, well-scoped migration ideal for an automated coding agent.

Summary

The Apple app still writes the deprecated PositionConfig.gps_enabled field on every Position config save. Per the upstream deprecated-fields audit, this field's successor is gps_mode = 13. This was a ⚠️ (partial) row rather than a clean red X: the app already reads gps_mode, but it also reads deviceGpsEnabled as a legacy-bridge fallback on load and, on every write, sets pc.gpsEnabled = gpsMode == 1 alongside pc.gpsMode — sending the deprecated field to all firmware versions regardless.

Field	Detail
Proto message	PositionConfig
Deprecated field	gps_enabled = 4
Deprecated since	gps_mode added v2.2.21 (2024-02-01); [deprecated=true] annotated v2.7.4
Stable	v2.7.15
Replacement	gps_mode = 13 (GpsMode enum: NOT_PRESENT / ENABLED / DISABLED)
Android status	✅ Not shown — PositionConfigScreen uses gps_mode exclusively
Apple status	⚠️ Written on every save

Audit reference

https://github.com/meshtastic/design/blob/master/standards/audits/deprecated-fields-audit.md

Suggested approach

1. Grep the Apple codebase for the Swift symbols (e.g. gpsEnabled, deviceGpsEnabled, gps_enabled, and gpsMode / gps_mode) and the Position config settings form / save path.
2. Stop writing gpsEnabled when saving PositionConfig — persist only gpsMode.
3. Keep backward-compat on read: continue tolerating gpsEnabled arriving from older firmware (the legacy-bridge fallback), but treat gpsMode as the source of truth; don't re-emit the deprecated field.
4. Verify saving Position config no longer sets gpsEnabled, and that reading a config from older firmware still maps correctly onto the GPS mode UI.