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/components/textInput.tsx

@@ -360,6 +360,10 @@ export function TextInput({
 
   const nativeCursor = focus && termFocus && !selected && !!stdout?.isTTY
 
+  // Placeholder text is just a hint, not a selection — render it dim
+  // without inverse styling. In a TTY the hardware cursor parks at column
+  // 0 and visually marks the input start. Non-TTY surfaces still need the
+  // synthetic inverse first-char to draw a cursor at all.
   const rendered = useMemo(() => {
     if (!focus) {
       return display || dim(placeholder)
@@ -711,6 +715,14 @@ export function TextInput({
     if (range && range.start === range.end) {
       selRef.current = null
       setSel(null)
+
+      return
+    }
+
+    const normalized = selRange()
+
+    if (isMac && normalized) {
+      void writeClipboardText(vRef.current.slice(normalized.start, normalized.end))
     }
   }