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/banner.ts

@@ -74,9 +74,9 @@ const LOGO_GRADIENT = [0, 0, 1, 1, 2, 2] as const
 const CADUC_GRADIENT = [2, 2, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 3, 3, 3] as const
 
 const colorize = (art: string[], gradient: readonly number[], c: ThemeColors): Line[] => {
-  const p = [c.gold, c.amber, c.bronze, c.dim]
+  const p = [c.primary, c.accent, c.border, c.muted]
 
-  return art.map((text, i) => [p[gradient[i]!] ?? c.dim, text])
+  return art.map((text, i) => [p[gradient[i]!] ?? c.muted, text])
 }
 
 export const LOGO_WIDTH = 98