[feat](trx-frontend-http): implement Phase 1 UX/UI quick wins from Settings analysis

- IX-2: Add confirm() dialogs before all destructive actions (10 history
  clear buttons, scheduler reset, background decode reset)
- IX-6: Add Select All / Deselect All buttons for background decode
  bookmark checklist
- IX-1: Add dirty-state indicator (pulsing dot) on Save buttons when
  unsaved changes exist in scheduler and background decode panels
- A-4: Add role="alert" and aria-live="polite" to toast notification
  elements for screen reader accessibility
- A-3: Add Unicode symbol prefixes to background decode state labels
  (checkmark/triangle/cross) so state is distinguishable without color

https://claude.ai/code/session_01ShfPMW9hPLD3czp9YovkbJ
Signed-off-by: Claude <noreply@anthropic.com>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/ft4.js

@@ -190,6 +190,7 @@ ft4DecodeToggleBtn?.addEventListener("click", async () => {
 });
 
 document.getElementById("settings-clear-ft4-history")?.addEventListener("click", async () => {
+  if (!confirm("Clear all FT4 decode history? This cannot be undone.")) return;
   try {
     await postPath("/clear_ft4_decode");
     window.resetFt4HistoryView();