fix(tui): honor documented mouse_tracking config key (#17188)

* fix(tui): honor documented mouse_tracking config key

The TUI runtime was reading display.tui_mouse while docs and user-facing
examples pointed users at display.mouse_tracking. That made persistent
mouse-disable config look like a no-op for users trying to restore native
terminal selection/copy behavior on Linux/SSH/tmux terminals.

Use display.mouse_tracking as the canonical key, keep display.tui_mouse as
a legacy fallback, and have /mouse write the documented key. Both gateway
config.get and client-side config sync now share the same precedence: the
canonical key wins, then the legacy key, then default on.

* review(copilot): align mouse tracking config coercion

- Load gateway config once before deriving display.mouse_tracking state.
- Use key-presence precedence on the TUI client too, so canonical
  mouse_tracking wins over legacy tui_mouse even when the value is null.
- Treat numeric 0 as disabled on both gateway and client, matching the
  existing string "0" handling.
- Widen ConfigDisplayConfig mouse fields because config.get full returns raw
  YAML, not normalized booleans.

ui-tui/src/__tests__/useConfigSync.test.ts

@@ -5,6 +5,7 @@ import {
   applyDisplay,
   normalizeBusyInputMode,
   normalizeIndicatorStyle,
+  normalizeMouseTracking,
   normalizeStatusBar
 } from '../app/useConfigSync.js'
 
@@ -70,6 +71,19 @@ describe('applyDisplay', () => {
     expect(s.sections).toEqual({})
   })
 
+  it('uses documented mouse_tracking with legacy tui_mouse fallback', () => {
+    const setBell = vi.fn()
+
+    applyDisplay({ config: { display: { mouse_tracking: false } } }, setBell)
+    expect($uiState.get().mouseTracking).toBe(false)
+
+    applyDisplay({ config: { display: { mouse_tracking: true, tui_mouse: false } } }, setBell)
+    expect($uiState.get().mouseTracking).toBe(true)
+
+    applyDisplay({ config: { display: { tui_mouse: false } } }, setBell)
+    expect($uiState.get().mouseTracking).toBe(false)
+  })
+
   it('parses display.sections into per-section overrides', () => {
     const setBell = vi.fn()
 
@@ -166,6 +180,19 @@ describe('normalizeStatusBar', () => {
   })
 })
 
+describe('normalizeMouseTracking', () => {
+  it('defaults on and prefers canonical mouse_tracking over legacy tui_mouse', () => {
+    expect(normalizeMouseTracking({})).toBe(true)
+    expect(normalizeMouseTracking({ mouse_tracking: false })).toBe(false)
+    expect(normalizeMouseTracking({ mouse_tracking: 0 })).toBe(false)
+    expect(normalizeMouseTracking({ mouse_tracking: 'off' })).toBe(false)
+    expect(normalizeMouseTracking({ mouse_tracking: 'false' })).toBe(false)
+    expect(normalizeMouseTracking({ mouse_tracking: null, tui_mouse: false })).toBe(true)
+    expect(normalizeMouseTracking({ mouse_tracking: true, tui_mouse: false })).toBe(true)
+    expect(normalizeMouseTracking({ tui_mouse: false })).toBe(false)
+  })
+})
+
 describe('normalizeBusyInputMode', () => {
   it('passes through the canonical CLI parity values', () => {
     expect(normalizeBusyInputMode('queue')).toBe('queue')