[feat](trx-frontend-http): per-rig bookmarks, scheduler, and decode filtering

Two-tier bookmark system: general bookmarks shared across all rigs plus
rig-specific bookmarks with scope picker in the Bookmarks tab. Scheduler
storage split into per-rig files with migration from legacy single file.
Decode history tagged with rig_id and filterable via ?remote= on
/decode/history endpoint. Decode SSE reconnects on rig switch to refresh
filtered history.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html

@@ -368,6 +368,9 @@
     </div>
     <div id="tab-bookmarks" class="tab-panel" style="display:none;">
       <div class="bm-toolbar">
+        <select id="bm-scope-picker" class="status-input" aria-label="Bookmark scope">
+          <option value="general">General</option>
+        </select>
         <select id="bm-category-filter" class="status-input" aria-label="Filter by category">
           <option value="">All categories</option>
         </select>