[feat](trx-rs): remap decoder modes — remove DIG/PKT from SDR, wire decoders to standard modes

For SDR backends, DIG and PKT are removed from supported_modes and
replaced by USB and FM respectively. CAT backends (FT-817, FT-450D)
retain DIG/PKT as before.

Decoder mode allowances updated:
- APRS: FM | PKT (was PKT only)
- HF-APRS: USB | DIG (was DIG only)
- AIS: AIS | FM | PKT (was AIS only)
- VDES: VDES | FM (was VDES only)
- FT8/FT4/FT2/WSPR: USB | DIG (unchanged)
- CW: CW | CWR (unchanged)
- LRPT: FM (unchanged, mode-independent)

Frontend status text, bookmark decoder toggles, background-decode
fallbacks, and scheduler wiring updated to match.

https://claude.ai/code/session_01DCAaMH8RF5FNB2gRtVu4pY
Signed-off-by: Claude <noreply@anthropic.com>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/bookmarks.js

@@ -428,9 +428,9 @@ async function bmApply(bm) {
         await postPath("/set_freq?hz=" + bm.freq_hz);
       }
     })();
-    // Decoder toggles (DIG / FM modes) — also fire-and-forget.
+    // Decoder toggles (USB / DIG / FM / PKT modes) — also fire-and-forget.
     const hasDecoders = Array.isArray(bm.decoders) && bm.decoders.length > 0;
-    const decoderMode = bm.mode === "DIG" || bm.mode === "FM";
+    const decoderMode = bm.mode === "USB" || bm.mode === "DIG" || bm.mode === "FM" || bm.mode === "PKT";
     const decoderPromise = (hasDecoders && decoderMode) ? (async () => {
       const statusResp = await fetch("/status");
       if (statusResp.ok) {