Add allowlisted macOS and Windows computer use

[naliazheli]

Restores #543. GitHub automatically closed the original PR when its source fork was temporarily made private. This replacement preserves the original change.

Summary

• add opt-in macOS and Windows Computer use settings with an explicit application allowlist
• accept validated .app bundles on macOS and exact .exe paths on Windows
• bundle pinned Cua Driver 0.22.0 builds with SHA-256 verification, vendor signature verification on macOS, and the MIT license
• guide macOS users through Accessibility and Screen Recording permission setup
• run Cua Driver with exact executable, PID, and window manifests and expose accessibility discovery, screenshots, app launch, click, text input, and key press tools
• keep the signed macOS application bundle immutable by writing the short-lived runtime manifest to the user's state directory

Security model

• disabled by default, with an empty allowlist
• exact application paths only; command interpreters and automation applications are rejected
• macOS bundles must contain a valid Info.plist, an executable Mach-O, and no escaping symlinks
• no coordinate-based click API
• interaction tools require fresh one-time element tokens whose labels are verified before action
• app launch, screenshot writes, clicks, typing, and key presses remain approval-gated
• no shell, arbitrary process, filesystem, or browser-profile capabilities are admitted
• Cua Driver telemetry is disabled; manifests are deny-by-default, expire after 8 hours, and use a 30-minute idle timeout
• runtime manifests are stored outside the signed app bundle with 0600 permissions on macOS

The bundled archives and checksums come from the official Cua Driver 0.22.0 release.

Screenshot

Verification

• 19 passed: focused backend connector/settings tests, including real macOS PID-to-executable resolution
• 136 passed: complete frontend unit suite
• npm run build
• cargo check
• full backend suite: 1877 passed, 1 skipped; 3 existing URL-guard tests fail only because this machine's proxy DNS maps public test domains to 198.18.x.x
• built a complete macOS DMG and verified the packaged Cua Driver 0.22.0 binaries are Cua AI-signed universal arm64 + x86_64 Mach-O files
• exercised the real driver against TextEdit: only the allowlisted window reached OpenWorker; a foreign visible window was filtered out before the model-facing result
• exercised the packaged server settings API: .app validation, driver reload, external 0600 runtime manifest, and unchanged in-bundle policy hash all passed