The sidebar search trigger, quick-create-issue modal, and feedback modal
hardcoded the Mac glyphs (⌘, ↵) for their keyboard hints, so Windows and
Linux users always saw Mac shortcuts even though the underlying handlers
already accept metaKey || ctrlKey.
Extract a small platform helper (isMac, modKey, enterKey, formatShortcut)
in packages/core/platform/keyboard.ts and route all four affected sites
(plus the editor bubble menu, which had the same logic inlined) through
it, so non-Mac users see Ctrl+K, Ctrl+Enter, etc.
Closesmultica-ai/multica#2056
