feat(hal): GPS PPS timestamp sync via lgw_gps_* for SX1303

[iceice400]

Summary

Follow-up to #65: adds Semtech HAL GPS/PPS bindings so the SX1302/SX1303 concentrator can align internal packet timestamp_us with GPS time on RAK Pi HATs (u-blox on /dev/ttyAMA0, PPS into the concentrator).

This is orthogonal to location.source: uart / gpsd, which only feed dashboard coordinates and NodeInfo.

Changes

HAL (src/hal/)

• sx1302_gps_types.py — TimespecS, TrefS, CoordS, GPS message constants.
• sx1302_gps_signatures.py + apply_gps_signatures() from apply_signatures().
• sx1302_gps.py — HalGpsPpsSync: lgw_gps_enable, background UBX/NMEA parser, lgw_gps_sync on UBX-NAV-TIMEGPS, sx1302_gps_enable, optional lgw_cnt2utc.
• SX1302Wrapper.start_gps_pps() / stop_gps_pps(); ConcentratorCaptureSource starts PPS after lgw_start() when configured.

Config

• radio.gps_pps_enabled, gps_pps_tty_path, gps_family, gps_pps_target_baud.
• validate_config_consistency() rejects gps_pps_enabled + location.source: uart on the same TTY.

API

• GET /api/device/gps-pps-status — sync count, last error, reference counter.
• radio_advanced in GET /api/config exposes PPS fields.

Docs

• CONFIGURATION.md — GPS PPS section + uart/PPS matrix.
• docs/plans/gps-pps-follow-up-issue.md — issue template for trackers.

Why

#65 fixed lgw_start() on RAK/SX1303 and wired UART for map GPS. Operators running SX1303 with PPS still need concentrator-time alignment for accurate packet timestamps — that path lives in lgw_gps_*, not in NMEA GGA parsing.

Operator notes

Need	Config
Live map from HAT UART	location.source: uart, gps_pps_enabled: false
PPS timestamps + USB gpsd map	location.source: gpsd, gps_pps_enabled: true
PPS only, fixed coords	location.source: static, gps_pps_enabled: true

Requires libloragw built with loragw_gps.c. If symbols are missing, Meshpoint logs once and continues without PPS.

Type

• Feature
• Hardware change
• Docs
• Bug fix
• UI (status API only; no dashboard card in this PR)

Testing

• Local unit tests
• Tested on RAK hardware (needs reviewer / field)

python -m unittest tests.test_hal_gps_pps tests.test_sx1302_wrapper_hal_guard -v

Depends on

• Best reviewed after feat: RAK/SX1303 HAL guard, UART onboard GPS, and operator docs #65 merges (stacked from the same fork branch family). Can rebase onto main once feat: RAK/SX1303 HAL guard, UART onboard GPS, and operator docs #65 lands.

Closes