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/app/interfaces.ts

@@ -41,7 +41,9 @@ export interface SelectionApi {
   captureScrolledRows: (firstRow: number, lastRow: number, side: 'above' | 'below') => void
   clearSelection: () => void
   copySelection: () => Promise<string>
+  copySelectionNoClear: () => Promise<string>
   getState: () => unknown
+  version: () => number
   shiftAnchor: (dRow: number, minRow: number, maxRow: number) => void
   shiftSelection: (dRow: number, minRow: number, maxRow: number) => void
 }