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

tests/cli/test_cli_skin_integration.py

@@ -40,14 +40,14 @@ class TestCliSkinPromptIntegration:
         cli = _make_cli_stub()
 
         set_active_skin("ares")
-        assert cli._get_tui_prompt_fragments() == [("class:prompt", "⚔ ❯ ")]
+        assert cli._get_tui_prompt_fragments() == [("class:prompt", "⚔ ")]
 
     def test_secret_prompt_fragments_preserve_secret_state(self):
         cli = _make_cli_stub()
         cli._secret_state = {"response_queue": object()}
 
         set_active_skin("ares")
-        assert cli._get_tui_prompt_fragments() == [("class:sudo-prompt", "🔑 ❯ ")]
+        assert cli._get_tui_prompt_fragments() == [("class:sudo-prompt", "🔑 ⚔ ")]
 
     def test_narrow_terminals_compact_voice_prompt_fragments(self):
         cli = _make_cli_stub()