[feat](trx-rs): add VDES decoder mode support

Add a new trx-vdes decoder path alongside AIS, wire VDES through the server/frontend decode pipeline, and fix the web map so AIS vessel symbols load correctly and the TRX receiver marker appears when location data arrives.

Co-authored-by: OpenAI Codex <codex@openai.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-server/trx-backend/trx-backend-ft817/src/lib.rs

@@ -196,6 +196,7 @@ impl Ft817 {
                     RigMode::WFM,
                     RigMode::FM,
                     RigMode::AIS,
+                    RigMode::VDES,
                     RigMode::DIG,
                     RigMode::PKT,
                 ],
@@ -589,7 +590,7 @@ fn encode_mode(mode: &RigMode) -> u8 {
         RigMode::AM => 0x04,
         RigMode::WFM => 0x06,
         RigMode::FM => 0x08,
-        RigMode::AIS => 0x08,
+        RigMode::AIS | RigMode::VDES => 0x08,
         RigMode::DIG => 0x0A,
         RigMode::PKT => 0x0C,
         RigMode::Other(_) => 0x00,