fix(tui): restore macOS copy behavior and theme polish (#17131)

This PR groups the TUI fixes that restore macOS Terminal usability and clean up the theme/composer regressions:

- copy transcript selections on macOS drag-release so Terminal.app users can copy while mouse tracking is enabled
- copy composer selections on macOS drag-release; composer selection is internal to TextInput and does not use the global Ink selection bus
- keep IDE Cmd+C forwarding setup macOS-only, and make keybinding conflict checks respect simple when-clause overlap/negation
- force truecolor before chalk initializes (unless NO_COLOR / FORCE_COLOR / HERMES_TUI_TRUECOLOR opt-outs apply) so the default banner keeps its gold/amber/bronze gradient in Terminal.app
- move TUI surfaces onto semantic theme tokens and preserve skin prompt symbols as bare tokens with renderer-owned spacing
- render focused placeholders as dim hint text in TTY mode instead of inverse/selected-looking synthetic cursor text

ui-tui/src/types/hermes-ink.d.ts

@@ -145,6 +145,7 @@ declare module '@hermes/ink' {
     readonly clearSelection: () => void
     readonly hasSelection: () => boolean
     readonly getState: () => unknown
+    readonly version: () => number
     readonly subscribe: (cb: () => void) => () => void
     readonly shiftAnchor: (dRow: number, minRow: number, maxRow: number) => void
     readonly shiftSelection: (dRow: number, minRow: number, maxRow: number) => void