[feat](trx-rs): remove MARINE mode (superseded by virtual channels)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-server/trx-backend/trx-backend-ft817/src/lib.rs

@@ -603,7 +603,7 @@ fn encode_mode(mode: &RigMode) -> Option<u8> {
         RigMode::FM => 0x08,
         RigMode::DIG => 0x0A,
         RigMode::PKT => 0x0C,
-        RigMode::AIS | RigMode::VDES | RigMode::MARINE | RigMode::Other(_) => return None,
+        RigMode::AIS | RigMode::VDES | RigMode::Other(_) => return None,
     })
 }