[feat](trx-rs): display APRS-IS connection status on About page

Thread aprs_is_status through RigState, RigSnapshot, and the protocol
layer following the same pattern as pskreporter_status. Show the
connection target and callsign when enabled, or "Disabled" otherwise.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/trx-protocol/src/codec.rs

@@ -427,6 +427,7 @@ mod tests {
             server_latitude: None,
             server_longitude: None,
             pskreporter_status: None,
+            aprs_is_status: None,
             aprs_decode_enabled: false,
             hf_aprs_decode_enabled: false,
             cw_decode_enabled: false,