[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/index.html

@@ -1074,7 +1074,7 @@
       </div>
       <div id="subtab-settings-scheduler" class="sub-tab-panel">
         <div id="scheduler-panel" class="sch-panel">
-          <div class="sch-toast" id="scheduler-toast" style="display:none;"></div>
+          <div class="sch-toast" id="scheduler-toast" role="alert" aria-live="polite" style="display:none;"></div>
           <!-- Now Playing status card (moved to top) -->
           <div class="now-playing-card">
             <div id="scheduler-status-card" class="sch-status-card">No activity yet.</div>
@@ -1254,7 +1254,7 @@
       </div>
       <div id="subtab-settings-background-decode" class="sub-tab-panel" style="display:none;">
         <div id="background-decode-panel" class="sch-panel">
-          <div class="sch-toast" id="background-decode-toast" style="display:none;"></div>
+          <div class="sch-toast" id="background-decode-toast" role="alert" aria-live="polite" style="display:none;"></div>
           <!-- Now Playing status card (moved to top) -->
           <div class="now-playing-card">
             <div id="background-decode-status-card" class="sch-status-card">No background decode bookmarks configured.</div>
@@ -1273,6 +1273,10 @@
               <label class="sch-label" style="min-width:100%;">Bookmarks
                 <input type="text" id="bgd-bookmark-filter" class="bgd-checklist-filter" placeholder="Filter bookmarks..." />
               </label>
+              <div class="bgd-select-actions">
+                <button type="button" id="bgd-select-all-btn" class="bgd-select-btn" aria-label="Select all bookmarks">Select All</button>
+                <button type="button" id="bgd-deselect-all-btn" class="bgd-select-btn" aria-label="Deselect all bookmarks">Deselect All</button>
+              </div>
               <div id="bgd-bookmark-checklist" class="bgd-checklist"></div>
             </div>
           </div>