feat(ingestor): store uplink pings (/uplink)

[efiten]

Summary

Ingestor side of uplink pings, so the data starts accumulating while the map layer is being built (separate PR). CoreDrive RX v1.21.0 sends cdrx <tag> on #coredrive, listens for repeaters re-broadcasting it, and reports UPLINK_PING on meshcore/client/{pk}/uplink.

• Handler: new uplink subtopic, gated on clientUplink.enabled (default off), stored in table client_uplink_pings (UNIQUE(rx_pubkey, tag)).
  • tag must be 8 hex characters.
  • pkt_hash must be 16 hex characters, otherwise it is dropped.
  • Echoes are validated and capped at 32.
  • GPS is optional.
• Tag to hash without an echo: the ingestor decrypts GRP_TXT on the ping channel itself and stores the tag with its packet hash in client_uplink_tx.
  • The channel's hash byte (0x76) is shared with busy unrelated channels, so the MAC check and the cdrx <tag> text decide.
  • The channel key is derived from clientUplink.channel and never added to the channel list.
• Retention: retention.clientUplinkDays covers both tables.
• Docs: contract in docs/client-rx-coverage.md, keys in config.example.json.

Performance

noteUplinkTransmission runs on the observer packet path only for GRP_TXT on hash byte 0x76 that the ingestor could not decrypt. That is one HMAC per such packet; on live there were dozens per hour on that byte. Everything else returns after a field compare.

Test plan

• go test ./... in cmd/ingestor: pass. New tests in client_uplink_test.go.
• Firmware match: #coredrive gives hash byte 0x76, as seen on air in the beta field test (transmission b76c6a2777f9b0e9, 15 observers).
• Live: clientUplink.enabled on, then a drive with CoreDrive uplinkPing on.

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