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/lib/syntax.ts

@@ -80,7 +80,7 @@ export function highlightLine(line: string, lang: string, t: Theme): Token[] {
   }
 
   if (spec.comment && line.trimStart().startsWith(spec.comment)) {
-    return [[t.color.dim, line]]
+    return [[t.color.muted, line]]
   }
 
   const tokens: Token[] = []
@@ -97,11 +97,11 @@ export function highlightLine(line: string, lang: string, t: Theme): Token[] {
     const ch = tok[0]!
 
     if (ch === '"' || ch === "'" || ch === '`') {
-      tokens.push([t.color.amber, tok])
+      tokens.push([t.color.accent, tok])
     } else if (ch >= '0' && ch <= '9') {
-      tokens.push([t.color.cornsilk, tok])
+      tokens.push([t.color.text, tok])
     } else if (spec.keywords.has(tok)) {
-      tokens.push([t.color.bronze, tok])
+      tokens.push([t.color.border, tok])
     } else {
       tokens.push(['', tok])
     }