fix(shortcuts): address review on rebinding (gate holes, re-enable/Reset duplicates, labels, tests)

- isUserBoundShortcutEvent skips toggleSessionSidebar (it has its own gate) and an
  entry re-captured onto its own default, so ^L still reaches the CLI.
- Re-enabling a shortcut and Reset run the duplicate check and refuse when the
  chord was taken meanwhile; Ctrl/Shift+Enter and Ctrl/Cmd+V are reserved with
  Alt+1-9, and the Alt-digit check no longer excludes Cmd.
- Alt+[ / Alt+] keep their Alt/Option+[ labels via displayBindings.
- Behavioural tests (vm harness) replace the source-string test.
- Docs: wiki Rebinding / Why-chords-behave-oddly, architecture-invariants note.
- Small: _shortcutActions indentation, stale Alt-block comment, typeof check
  instead of Object.hasOwn, full-width parentheses in zh-CN.

.changeset/keybinding-polish.md

@@ -2,4 +2,4 @@
 'aicodeman': minor
 ---
 
-Shortcut rebinding (App Settings → Shortcuts) now covers Previous Session and the alternate Next Session, which were fixed at Alt/Option+[ and Alt/Option+]. Capturing a chord another action already owns is refused with a message naming that action (Alt+1-9 are reserved for tab switching). A chord you rebound to an app action no longer also types into the terminal: a rebind to Alt+J used to switch tabs and send ESC j to the session as well.
+Shortcut rebinding (App Settings → Shortcuts) now covers Previous Session and the alternate Next Session, which were fixed at Alt/Option+[ and Alt/Option+]. Capturing a chord another action already owns is refused with a message naming that action (Alt+1-9 are reserved for tab switching, Ctrl/Shift+Enter for newline and Ctrl/Cmd+V for paste); re-enabling a disabled shortcut and Reset run the same check. A chord you rebound to an app action no longer also types into the terminal: a rebind to Alt+J used to switch tabs and send ESC j to the session as well.