Document dev environment setup for SwiftApp (macOS/Xcode-only)

[aj327]

What

Adds AGENTS.md documenting how to set up, build, and run this project, and records the Cloud Agent limitation.

Why

SwiftApp is a UIKit iOS app (SDKROOT = iphoneos, iOS 10.3, Swift 3.0, import UIKit, storyboards) built with Xcode. It can only be built and run on macOS with Xcode + the iOS Simulator.

The Cursor Cloud Agent VM is Ubuntu Linux, where:

• Xcode is unavailable and cannot run.
• UIKit / the iphoneos SDK do not exist (even the open-source Swift-for-Linux toolchain lacks UIKit).
• The Swift-for-Linux download is blocked by network egress on this VM.
• There is no test target (scheme Testables is empty), no linter config, and no dependency manager.

As a result, the app cannot be built, run, linted, or tested on the Linux Cloud Agent VM. This is a hard platform limitation, not a configuration issue.

Changes

• Add AGENTS.md with project layout, macOS/Xcode build/run commands, and a ## Cursor Cloud specific instructions section explaining the Linux limitation.
• Update script recorded as a no-op (nothing to install on Linux).