[feat](trx-reporting): add APRS-IS position beaconing

Add periodic IGate position beacon support to the APRS-IS uplink.
New AprsFiConfig fields: beacon (bool), beacon_interval_secs (default
1200), beacon_symbol (default "/-"), latitude/longitude overrides.

A beacon is sent immediately on connect then every beacon_interval_secs.
Coordinates fall back from [aprsfi] to [general].latitude/longitude.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-server/src/main.rs

@@ -520,7 +520,7 @@ fn spawn_rig_audio_stack(
             let ai_shutdown_rx = shutdown_rx.clone();
             handles.push(tokio::spawn(async move {
                 tokio::select! {
-                    _ = trx_reporting::aprsfi::run_aprsfi_uplink(ai_cfg, cs, ai_decode_rx) => {}
+                    _ = trx_reporting::aprsfi::run_aprsfi_uplink(ai_cfg, cs, latitude, longitude, ai_decode_rx) => {}
                     _ = wait_for_shutdown(ai_shutdown_rx) => {}
                 }
             }));