feat: enable Computer Use with macOS + Windows + Linux support

Phase 1: Replace @ant/computer-use-mcp stub (12 files, 6517 lines).

Phase 2: Remove 8 macOS-only guards in src/:
- main.tsx: remove getPlatform()==='macos' check
- swiftLoader.ts: remove darwin-only throw
- executor.ts: extend platform guard, clipboard dispatch, paste key
- drainRunLoop.ts: skip CFRunLoop pump on non-darwin
- escHotkey.ts: non-darwin returns false (Ctrl+C fallback)
- hostAdapter.ts: non-darwin permissions granted
- common.ts: dynamic platform + screenshotFiltering
- gates.ts: enabled:true, subscription check removed

Phase 3: Add Linux backends (xdotool/scrot/xrandr/wmctrl):
- computer-use-input/backends/linux.ts (173 lines)
- computer-use-swift/backends/linux.ts (278 lines)

Verified on Windows x64: mouse, screenshot, displays, foreground app.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/@ant/computer-use-mcp/src/executor.ts

@@ -0,0 +1,111 @@
+export interface DisplayGeometry {
+  displayId: number
+  width: number
+  height: number
+  scaleFactor: number
+  originX: number
+  originY: number
+}
+
+export interface ScreenshotResult {
+  base64: string
+  width: number
+  height: number
+  displayWidth: number
+  displayHeight: number
+  originX: number
+  originY: number
+  displayId?: number
+}
+
+export interface FrontmostApp {
+  bundleId: string
+  displayName: string
+}
+
+export interface InstalledApp {
+  bundleId: string
+  displayName: string
+  path: string
+  iconDataUrl?: string
+}
+
+export interface RunningApp {
+  bundleId: string
+  displayName: string
+  pid?: number
+}
+
+export interface ResolvePrepareCaptureResult extends ScreenshotResult {
+  hidden: string[]
+  activated?: string
+  displayId: number
+}
+
+export interface ComputerExecutorCapabilities {
+  screenshotFiltering: 'native' | 'none'
+  platform: 'darwin' | 'win32'
+  hostBundleId: string
+}
+
+export interface ComputerExecutor {
+  capabilities: ComputerExecutorCapabilities
+  prepareForAction(
+    allowlistBundleIds: string[],
+    displayId?: number,
+  ): Promise<string[]>
+  previewHideSet(
+    allowlistBundleIds: string[],
+    displayId?: number,
+  ): Promise<Array<{ bundleId: string; displayName: string }>>
+  getDisplaySize(displayId?: number): Promise<DisplayGeometry>
+  listDisplays(): Promise<DisplayGeometry[]>
+  findWindowDisplays(
+    bundleIds: string[],
+  ): Promise<Array<{ bundleId: string; displayIds: number[] }>>
+  resolvePrepareCapture(opts: {
+    allowedBundleIds: string[]
+    preferredDisplayId?: number
+    autoResolve: boolean
+    doHide?: boolean
+  }): Promise<ResolvePrepareCaptureResult>
+  screenshot(opts: {
+    allowedBundleIds: string[]
+    displayId?: number
+  }): Promise<ScreenshotResult>
+  zoom(
+    regionLogical: { x: number; y: number; w: number; h: number },
+    allowedBundleIds: string[],
+    displayId?: number,
+  ): Promise<{ base64: string; width: number; height: number }>
+  key(keySequence: string, repeat?: number): Promise<void>
+  holdKey(keyNames: string[], durationMs: number): Promise<void>
+  type(text: string, opts: { viaClipboard: boolean }): Promise<void>
+  readClipboard(): Promise<string>
+  writeClipboard(text: string): Promise<void>
+  moveMouse(x: number, y: number): Promise<void>
+  click(
+    x: number,
+    y: number,
+    button: 'left' | 'right' | 'middle',
+    count: 1 | 2 | 3,
+    modifiers?: string[],
+  ): Promise<void>
+  mouseDown(): Promise<void>
+  mouseUp(): Promise<void>
+  getCursorPosition(): Promise<{ x: number; y: number }>
+  drag(
+    from: { x: number; y: number } | undefined,
+    to: { x: number; y: number },
+  ): Promise<void>
+  scroll(x: number, y: number, dx: number, dy: number): Promise<void>
+  getFrontmostApp(): Promise<FrontmostApp | null>
+  appUnderPoint(
+    x: number,
+    y: number,
+  ): Promise<{ bundleId: string; displayName: string } | null>
+  listInstalledApps(): Promise<InstalledApp[]>
+  getAppIcon(path: string): Promise<string | undefined>
+  listRunningApps(): Promise<RunningApp[]>
+  openApp(bundleId: string): Promise<void>
+}