feat(ui): add R/F/D action shortcuts and unify keycap hint style

- Bind R=refresh, F=fetch metadata, D=download in PageControls via
  eventManager (plain letters only, skipped while typing or when a
  modal is open); triggers reuse the buttons' existing click handlers
- Show key-hint chips on the refresh/fetch/download/bulk toolbar
  buttons; convert the bulk chip to a semantic <kbd>
- Redesign shortcut hints as a neutral theme-adaptive keycap:
  --shortcut-* variables in base.css now derive from --text-muted
  with a bottom-edge shadow, shared by the toolbar chips, the header
  search cue, the help-modal cheat sheet, and onboarding key hints
- Add shared isTypingContext() helper to uiHelpers
- Add an Actions group (R/F/D) to the Shortcuts cheat-sheet tab

Verified with vitest (926 passing, incl. 6 new shortcut cases) and a
sandboxed E2E run in real Chrome (light/dark rendering, hover state,
'?' opening the Shortcuts tab, clean console)

templates/components/modals/help_modal.html

@@ -165,6 +165,24 @@
                     </ul>
                 </div>
 
+                <div class="shortcuts-section">
+                    <h4><i class="fas fa-bolt"></i> {{ t('help.shortcuts.groups.actions') }}</h4>
+                    <ul class="shortcuts-list">
+                        <li>
+                            <span class="shortcut-keys"><kbd>R</kbd></span>
+                            <span class="shortcut-description">{{ t('help.shortcuts.entries.refresh') }}</span>
+                        </li>
+                        <li>
+                            <span class="shortcut-keys"><kbd>F</kbd></span>
+                            <span class="shortcut-description">{{ t('help.shortcuts.entries.fetchMetadata') }}</span>
+                        </li>
+                        <li>
+                            <span class="shortcut-keys"><kbd>D</kbd></span>
+                            <span class="shortcut-description">{{ t('help.shortcuts.entries.downloadModel') }}</span>
+                        </li>
+                    </ul>
+                </div>
+
                 <div class="shortcuts-section">
                     <h4><i class="fas fa-object-group"></i> {{ t('help.shortcuts.groups.selection') }}</h4>
                     <ul class="shortcuts-list">