feat: add Swift language-specific rules

Add 5 rule files for Swift following the established pattern used by
TypeScript, Python, and Go rule sets. Covers Swift 6 strict concurrency,
Swift Testing framework, protocol-oriented patterns, Keychain-based
secret management, and SwiftFormat/SwiftLint hooks.

rules/swift/hooks.md

@@ -0,0 +1,20 @@
+---
+paths:
+  - "**/*.swift"
+  - "**/Package.swift"
+---
+# Swift Hooks
+
+> This file extends [common/hooks.md](../common/hooks.md) with Swift specific content.
+
+## PostToolUse Hooks
+
+Configure in `~/.claude/settings.json`:
+
+- **SwiftFormat**: Auto-format `.swift` files after edit
+- **SwiftLint**: Run lint checks after editing `.swift` files
+- **swift build**: Type-check modified packages after edit
+
+## Warning
+
+Flag `print()` statements — use `os.Logger` or structured logging instead for production code.