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/domain/roles.ts

@@ -2,8 +2,8 @@ import type { Theme } from '../theme.js'
 import type { Role } from '../types.js'
 
 export const ROLE: Record<Role, (t: Theme) => { body: string; glyph: string; prefix: string }> = {
-  assistant: t => ({ body: t.color.cornsilk, glyph: t.brand.tool, prefix: t.color.bronze }),
-  system: t => ({ body: '', glyph: '·', prefix: t.color.dim }),
-  tool: t => ({ body: t.color.dim, glyph: '⚡', prefix: t.color.dim }),
+  assistant: t => ({ body: t.color.text, glyph: t.brand.tool, prefix: t.color.border }),
+  system: t => ({ body: '', glyph: '·', prefix: t.color.muted }),
+  tool: t => ({ body: t.color.muted, glyph: '⚡', prefix: t.color.muted }),
   user: t => ({ body: t.color.label, glyph: t.brand.prompt, prefix: t.color.label })
 }