[feat](trx-rs): remove MARINE mode (superseded by virtual channels)

MARINE was a composite mode that ran both AIS and VDES decoders
simultaneously. It is now fully replaced by allocating two virtual
channels — one tuned to the AIS frequencies and one to VDES — each
decoded independently.

- trx-core/state: remove RigMode::MARINE variant
- trx-protocol/codec: remove MARINE parse/serialize
- trx-backend-ft817: remove MARINE from unsupported-mode guard
- trx-backend-ft450d: remove MARINE from FM CAT code mapping
- trx-backend-soapysdr: remove MARINE from bandwidth table, supported
  modes list, AIS channel activity check, parse_rig_mode, vchan_impl
  bandwidth table, demod selection, dsp/channel bandwidth / sample-rate
  / IQ-tap guards
- trx-server/audio: remove MARINE from AIS and VDES decoder activation
- trx-server/rig_task: remove MARINE from audio-streaming mode list
- trx-server/main: remove MARINE from bandwidth table, mode parser,
  VDES channel subscription match
- app.js: remove isMarineMode(), MARINE entry in MODE_BW_SPECS, MARINE
  bandwidth specs block in visibleBandwidthSpecs(), MARINE from
  decoder status mode lists, MARINE BW-edge drag guard

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

src/trx-protocol/src/codec.rs

@@ -24,7 +24,6 @@ pub fn parse_mode(s: &str) -> RigMode {
         "WFM" => RigMode::WFM,
         "AIS" => RigMode::AIS,
         "VDES" => RigMode::VDES,
-        "MARINE" => RigMode::MARINE,
         "DIG" | "DIGI" => RigMode::DIG,
         "PKT" | "PACKET" => RigMode::PKT,
         other => RigMode::Other(other.to_string()),
@@ -46,7 +45,6 @@ pub fn mode_to_string(mode: &RigMode) -> String {
         RigMode::WFM => "WFM".to_string(),
         RigMode::AIS => "AIS".to_string(),
         RigMode::VDES => "VDES".to_string(),
-        RigMode::MARINE => "MARINE".to_string(),
         RigMode::DIG => "DIG".to_string(),
         RigMode::PKT => "PKT".to_string(),
         RigMode::Other(s) => s.clone(),