feat(ui): land the centralized shortcuts core from #2532 with review fixes

The schema/config/bindings/registry/dispatcher module, useKeybind hooks,
recording dialog, reworked shortcuts settings page, help dialog, and the
localized action labels — re-based onto current main rather than merged
(the branch predates 440+ commits including the session-tabs shortcuts).

Review fixes applied on top of the original:
- close_session_tab (alt+w) joins the schema with labels in every locale;
  it shipped on main after the PR's base and would otherwise silently die.
- switch_context_surface's special-case in conflict resolution is now a
  declared prefixStyle config property instead of a magic id string.
- Duplicate handler registration warns in dev builds.
- The risky-browser-shortcut warning inspects every chord and covers
  mod+q/d/h/j/o/u plus mod+shift+w/q.
- The dispatcher remembers which target armed a two-chord prefix so the
  window-level completion handler can distinguish a deliberate sequence
  from typing in an editable field (guard lands with the dispatch hook).
- Schema tests: unique normalized default bindings enforced, and the
  flat-file-era override format proven to keep resolving.

packages/ui/src/lib/i18n/messages/ko.ts

@@ -1670,7 +1670,7 @@ export const dict: Record<I18nKey, string> = {
   'rightSidebar.contextNotesTodo.toast.planImported': '플랜 가져옴',
   'rightSidebar.contextNotesTodo.toast.readPlanFileFailed': '플랜 파일 읽기 실패',
   'inlineComment.range.lines': '줄 {start}-{end}',
-  'inlineComment.input.placeholder': '댓글 추가… (Cmd+Enter로 저장)',
+    'inlineComment.input.placeholder': '댓글 추가… ({shortcut}로 저장)',
   'inlineComment.input.placeholderShort': '댓글 추가…',
   'inlineComment.actions.cancel': '취소',
   'inlineComment.actions.save': '저장',