Add SwiftLint in CI

[austin-smith]

Goal

Add SwiftLint as a CI-only quality check.

Requirements

• Pin SwiftLint 0.65.0 and verify its checksum.
• Lint the app, unit tests, and UI tests before builds and tests run.
• Run SwiftLint in strict mode.
• Allow files up to 800 lines.
• Temporarily ignore only the file_length rule for:
  • ComputerSolitaire/Views/Shared/ContentView.swift
  • ComputerSolitaire/Views/Cards/Styles/PixelCardViews.swift
• Keep all other rules active for those two files.
• Disable the todo rule.
• Do not enable no_empty_block.
• Enable only these opt-in rules:
  • accessibility_label_for_image
  • accessibility_trait_for_button
  • async_without_await
  • balanced_xctest_lifecycle
  • discarded_notification_center_observer
  • force_unwrapping
  • unhandled_throwing_task
• Do not add a baseline, broad exclusions, or blanket suppressions.
• Do not remove useful comments or documentation to satisfy lint.
• Do not add Xcode integration or local build requirements.
• Track removal of the two file-length exceptions in Resolve SwiftLint file-length exceptions #36.

Validation

• SwiftLint reports zero violations.
• macOS and iOS Simulator builds pass.
• The macOS test suite passes.