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/hermes_cli/test_skin_engine.py

@@ -252,7 +252,7 @@ class TestCliBrandingHelpers:
         from hermes_cli.skin_engine import set_active_skin, get_active_prompt_symbol
 
         set_active_skin("ares")
-        assert get_active_prompt_symbol() == "⚔ ❯ "
+        assert get_active_prompt_symbol() == "⚔ "
 
     def test_active_help_header_ares(self):
         from hermes_cli.skin_engine import set_active_skin, get_active_help_header