[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/style.css

@@ -4502,6 +4502,21 @@ button:focus-visible, input:focus-visible, select:focus-visible {
   border-color: var(--accent-green);
   font-weight: 700;
 }
+.sch-save-btn.sch-dirty::after {
+  content: "";
+  display: inline-block;
+  width: 7px;
+  height: 7px;
+  border-radius: 50%;
+  background: #fff;
+  margin-left: 0.45rem;
+  vertical-align: middle;
+  animation: sch-dirty-pulse 1.5s ease-in-out infinite;
+}
+@keyframes sch-dirty-pulse {
+  0%, 100% { opacity: 1; }
+  50% { opacity: 0.4; }
+}
 .sch-status-card {
   font-size: 0.9rem;
   color: var(--text-muted);
@@ -4829,6 +4844,26 @@ button:focus-visible, input:focus-visible, select:focus-visible {
   color: var(--text-muted);
   font-size: 0.85rem;
 }
+/* ── Select All / Deselect All buttons ────────────────────────────── */
+.bgd-select-actions {
+  display: flex;
+  gap: 0.5rem;
+}
+.bgd-select-btn {
+  background: var(--bg-secondary);
+  border: 1px solid var(--border-light);
+  border-radius: 0.3rem;
+  color: var(--text-muted);
+  font-size: 0.78rem;
+  font-weight: 600;
+  padding: 0.25rem 0.65rem;
+  cursor: pointer;
+  transition: background 0.15s, color 0.15s;
+}
+.bgd-select-btn:hover {
+  background: var(--card-bg);
+  color: var(--text);
+}
 /* ── SVG State Dot Badges ─────────────────────────────────────────── */
 .bgd-state-dot {
   width: 8px;