[feat](trx-rs): remove MARINE mode (superseded by virtual channels)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-core/src/rig/state.rs

@@ -76,7 +76,6 @@ pub enum RigMode {
     FM,
     AIS,
     VDES,
-    MARINE,
     DIG,
     PKT,
     Other(String),