[feat](trx-rs): configurable DIG sideband for SDR (auto/USB/LSB)

DIG has no inherent sideband; on the SDR backend it was always demodulated
as USB. Make it resolve to USB or LSB via a policy that defaults to the
amateur SSB/data convention (USB at/above 10 MHz, LSB below) and can be
overridden globally from the advanced radio controls or per-bookmark.

Design: the logical DIG mode is kept in RigState (display, decoder gating)
while the SDR pipeline is handed a concrete USB/LSB demodulator resolved from
(policy, dial frequency). Resolution happens at the boundary — the rig for
the primary channel and the virtual-channel manager for vchans — so the hot
DSP/demod path is untouched. The resolved sideband is only re-pushed when it
actually changes (e.g. tuning DIG/Auto across 10 MHz), keeping ordinary
tuning glitch-free.

Core/protocol:
- New `DigSidebandPolicy { Auto, Usb, Lsb }` with `resolve(freq)` and an
  `effective_demod_mode()` helper (trx-core), re-exported at the crate root.
- `RigCommand::SetSdrDigSideband`, `RigSdr::set_sdr_dig_sideband`, and a
  `RigFilterState.sdr_dig_sideband` field for state sync; wired through the
  ClientCommand mapping.

Config: `[rig.sdr] dig_sideband = "auto"` (regenerated trx-rs.toml.example).

SDR backend: the vchan manager owns the shared policy (atomic); the rig
applies it to the primary channel and, on `set_sdr_dig_sideband`, re-resolves
all DIG virtual channels.

Frontend: a mode-gated "DIG sideband" selector in the SDR advanced controls
(POST /set_sdr_dig_sideband), reflecting server state; bookmarks gain an
optional `dig_sideband` field (form selector shown only for DIG) that, on
apply, sets the global policy before switching to DIG. The scheduler honours
it for automated bookmark activation too.

Tests: policy resolution / effective-mode / u8+parse round-trips (trx-core);
a vchan integration test asserting a DIG channel resolves to LSB below
10 MHz, flips with the policy, and still lists as DIG.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UiK871ht2uPFBHtMbxy3wD
Signed-off-by: Stan Grams <sjg@haxx.space>

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

@@ -214,6 +214,12 @@ function bmBuildDecoderCheckboxes() {
     container.appendChild(label);
   });
 }
+function bmSyncDigSidebandVisibility() {
+  const label = bmOptionalEl("bm-dig-sideband-label");
+  if (!label) return;
+  const mode = (bmEl("bm-mode").value || "").trim().toUpperCase();
+  label.style.display = mode === "DIG" ? "" : "none";
+}
 function bmOpenForm(bm) {
   const wrap = bmEl("bm-form-wrap");
   if (!wrap) return;
@@ -227,7 +233,9 @@ function bmOpenForm(bm) {
   bmEl("bm-locator").value = bm ? bm.locator || "" : "";
   bmEl("bm-category-input").value = bm ? bm.category || "" : "";
   bmEl("bm-comment").value = bm ? bm.comment || "" : "";
+  bmEl("bm-dig-sideband").value = bm ? bm.dig_sideband || "" : "";
   bmWriteDecoders(bm?.decoders ?? []);
+  bmSyncDigSidebandVisibility();
   bmEl("bm-form-title").textContent = bm ? "Edit Bookmark" : "Add Bookmark";
   wrap.style.display = "flex";
   bmEl("bm-name").focus();
@@ -263,6 +271,7 @@ async function bmSave(e) {
   const category = bmEl("bm-category-input").value.trim();
   const comment = bmEl("bm-comment").value.trim();
   const decoders = bmReadDecoders();
+  const dig_sideband = mode.toUpperCase() === "DIG" ? bmEl("bm-dig-sideband").value || null : null;
   const formError = bmEl("bm-form-error");
   if (formError) formError.textContent = "";
   if (!name || !Number.isFinite(freq_hz) || !mode) {
@@ -279,7 +288,8 @@ async function bmSave(e) {
     locator: locator || null,
     category,
     comment,
-    decoders
+    decoders,
+    dig_sideband
   };
   try {
     let resp;
@@ -344,6 +354,12 @@ function bmApply(bm) {
     }
     const tunePromise = (async () => {
       await bridge.trx.modules.vchan?.takeSchedulerControl();
+      if ((bm.mode || "").toUpperCase() === "DIG" && bm.dig_sideband) {
+        const p = bm.dig_sideband.toLowerCase();
+        if (p === "auto" || p === "usb" || p === "lsb") {
+          await hostCore.postPath("/set_sdr_dig_sideband?policy=" + encodeURIComponent(p));
+        }
+      }
       const onVirtual = await bridge.trx.modules.vchan?.interceptMode(bm.mode) ?? false;
       if (!onVirtual) {
         await hostCore.postPath("/set_mode?mode=" + encodeURIComponent(bm.mode));
@@ -596,6 +612,7 @@ function bmPopulateScopePicker() {
   bmEl("bm-form").addEventListener("submit", (event) => {
     void bmSave(event);
   });
+  bmEl("bm-mode").addEventListener("input", bmSyncDigSidebandVisibility);
   bmEl("bm-form-cancel").addEventListener("click", bmCloseForm);
   const formWrap = bmEl("bm-form-wrap");
   if (formWrap) {