fix(tui): use command shortcuts on macOS

Make the Ink TUI match macOS keyboard expectations: Command handles copy and common editor/session shortcuts, while Control remains reserved for interrupt/cancel flows. Update the visible hotkey help to show platform-appropriate labels.

ui-tui/src/lib/platform.ts

@@ -0,0 +1,19 @@
+/** Platform-aware keybinding helpers.
+ *
+ * On macOS the "action" modifier is Cmd (key.meta in Ink), on other platforms
+ * it is Ctrl.  Ctrl+C is ALWAYS the interrupt key regardless of platform —
+ * it must never be remapped to copy.
+ */
+
+export const isMac = process.platform === 'darwin'
+
+/** The display label for the action modifier key. */
+export const modLabel = isMac ? '⌘' : 'Ctrl'
+
+/** True when the platform action-modifier is pressed (Cmd on macOS, Ctrl elsewhere). */
+export const isActionMod = (key: { ctrl: boolean; meta: boolean }): boolean =>
+  isMac ? key.meta : key.ctrl
+
+/** Match action-modifier + a single character (case-insensitive). */
+export const isAction = (key: { ctrl: boolean; meta: boolean }, ch: string, target: string): boolean =>
+  isActionMod(key) && ch.toLowerCase() === target