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/__tests__/theme.test.ts

@@ -44,7 +44,7 @@ describe('DEFAULT_THEME', () => {
   it('has color palette', async () => {
     const { DEFAULT_THEME } = await importThemeWithCleanEnv()
 
-    expect(DEFAULT_THEME.color.gold).toBe('#FFD700')
+    expect(DEFAULT_THEME.color.primary).toBe('#FFD700')
     expect(DEFAULT_THEME.color.error).toBe('#ef5350')
   })
 })
@@ -53,9 +53,9 @@ describe('LIGHT_THEME', () => {
   it('avoids bright-yellow accents unreadable on white backgrounds (#11300)', async () => {
     const { LIGHT_THEME } = await importThemeWithCleanEnv()
 
-    expect(LIGHT_THEME.color.gold).not.toBe('#FFD700')
-    expect(LIGHT_THEME.color.amber).not.toBe('#FFBF00')
-    expect(LIGHT_THEME.color.dim).not.toBe('#B8860B')
+    expect(LIGHT_THEME.color.primary).not.toBe('#FFD700')
+    expect(LIGHT_THEME.color.accent).not.toBe('#FFBF00')
+    expect(LIGHT_THEME.color.muted).not.toBe('#B8860B')
     expect(LIGHT_THEME.color.statusWarn).not.toBe('#FFD700')
   })
 
@@ -180,13 +180,22 @@ describe('fromSkin', () => {
   it('overrides banner colors', async () => {
     const { fromSkin } = await importThemeWithCleanEnv()
 
-    expect(fromSkin({ banner_title: '#FF0000' }, {}).color.gold).toBe('#FF0000')
+    expect(fromSkin({ banner_title: '#FF0000' }, {}).color.primary).toBe('#FF0000')
   })
 
   it('preserves unset colors', async () => {
     const { DEFAULT_THEME, fromSkin } = await importThemeWithCleanEnv()
 
-    expect(fromSkin({ banner_title: '#FF0000' }, {}).color.amber).toBe(DEFAULT_THEME.color.amber)
+    expect(fromSkin({ banner_title: '#FF0000' }, {}).color.accent).toBe(DEFAULT_THEME.color.accent)
+  })
+
+  it('derives completion current background from resolved completion background', async () => {
+    const { fromSkin } = await importThemeWithCleanEnv()
+
+    const theme = fromSkin({ banner_accent: '#000000', completion_menu_bg: '#ffffff' }, {})
+
+    expect(theme.color.completionBg).toBe('#ffffff')
+    expect(theme.color.completionCurrentBg).toBe('#bfbfbf')
   })
 
   it('overrides branding', async () => {
@@ -197,6 +206,14 @@ describe('fromSkin', () => {
     expect(brand.prompt).toBe('$')
   })
 
+  it('normalizes skin prompt symbols to trimmed single-line text', async () => {
+    const { DEFAULT_THEME, fromSkin } = await importThemeWithCleanEnv()
+
+    expect(fromSkin({}, { prompt_symbol: ' ⚔ ❯ \n' }).brand.prompt).toBe('⚔ ❯')
+    expect(fromSkin({}, { prompt_symbol: ' Ψ > \n' }).brand.prompt).toBe('Ψ >')
+    expect(fromSkin({}, { prompt_symbol: '\n\t' }).brand.prompt).toBe(DEFAULT_THEME.brand.prompt)
+  })
+
   it('defaults for empty skin', async () => {
     const { DEFAULT_THEME, fromSkin } = await importThemeWithCleanEnv()