test: add SPM + Xcode-app integration harnesses for the a11y-scan plugin

[Crash0v3rrid3]

What

Adds a tests/ folder with two consumer harnesses that integrate this repo's a11y-scan command plugin (via a path dependency on the repo root, ../..) and run accessibility scans over sample sources containing intentional issues.

tests/
├── README.md
├── spm/          # SwiftPM package consumer
└── xcode-app/    # Xcode iOS app (XcodeGen)

tests/spm/ — SwiftPM consumer

• Declares the AccessibilityDevTools dependency and invokes the command plugin via swift package plugin … scan (scripts/run-a11y-scan.sh).
• Sample SwiftUI views with intentional a11y issues; an XCTest unit test plus a credential-gated end-to-end scan test (RUN_A11Y_SCAN=1).
• The plugin is intentionally not attached to a target's plugins: array — a11y-scan is a command plugin (not build-tool), and attaching it makes swift build fail with "Plugin is declared with the buildTool capability…".

tests/xcode-app/ — Xcode app

• An iOS app described by an XcodeGen project.yml, so the generated .xcodeproj is gitignored.
• Runs the scan from a pre-compile build phase (the official Xcode integration), backed by a minimal Package.swift scan driver. Unit-test target included. ENABLE_USER_SCRIPT_SANDBOXING disabled so the scan can write ~/.cache.

Both harnesses skip/no-op without BROWSERSTACK_USERNAME / BROWSERSTACK_ACCESS_KEY, so builds and tests stay green.

Verification

• tests/spm: swift build ✅, swift test ✅ (unit test passes, scan test skips by default); swift package plugin --list shows 'scan' (plugin 'a11y-scan' in package 'AccessibilityDevTools').
• tests/xcode-app: project.yml validates as YAML; scan driver resolves and exposes the plugin; both shell scripts pass bash -n.
• ⚠️ Not run in this environment: xcodegen generate + xcodebuild test (xcodegen/Xcode simulator unavailable) and a live scan (needs BrowserStack creds). Generate and run locally to validate on your toolchain.

🤖 Generated with Claude Code