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)

locales/zh-CN.json

@@ -1977,6 +1977,7 @@
             "title": "[TODO: Translate] Keyboard & Mouse Shortcuts",
             "groups": {
                 "general": "[TODO: Translate] General",
+                "actions": "[TODO: Translate] Actions",
                 "selection": "[TODO: Translate] Selection & Bulk Mode",
                 "navigation": "[TODO: Translate] Navigation",
                 "modelModal": "[TODO: Translate] Model / Recipe Modal",
@@ -1993,6 +1994,9 @@
                 "focusSearch": "[TODO: Translate] Focus search",
                 "closeModal": "[TODO: Translate] Close modal / panel",
                 "openShortcuts": "[TODO: Translate] Open this shortcuts panel",
+                "refresh": "[TODO: Translate] Refresh model list",
+                "fetchMetadata": "[TODO: Translate] Fetch metadata from CivitAI (model pages only)",
+                "downloadModel": "[TODO: Translate] Download a model (model pages only)",
                 "toggleBulkMode": "[TODO: Translate] Toggle bulk mode",
                 "selectAll": "[TODO: Translate] Select all visible models",
                 "rangeSelect": "[TODO: Translate] Range select",