chore: add agentic tooling, cleanup

.crosslink/rules/swift.md

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+### Swift Best Practices
+
+#### Code Style
+- Follow Swift API Design Guidelines
+- Use `camelCase` for variables/functions, `PascalCase` for types
+- Prefer `let` over `var` when possible
+- Use optionals properly; avoid force unwrapping
+
+```swift
+// GOOD: Safe optional handling
+func findUser(id: String) -> User? {
+    guard let user = repository.find(id) else {
+        return nil
+    }
+    return user
+}
+
+// Using optional binding
+if let user = findUser(id: "123") {
+    print(user.name)
+}
+
+// BAD: Force unwrapping
+let user = findUser(id: "123")!  // Crash if nil
+```
+
+#### Error Handling
+- Use `throws` for recoverable errors
+- Use `Result<T, Error>` for async operations
+- Handle all error cases explicitly
+
+```swift
+// GOOD: Proper error handling
+func loadConfig() throws -> Config {
+    let data = try Data(contentsOf: configURL)
+    return try JSONDecoder().decode(Config.self, from: data)
+}
+
+do {
+    let config = try loadConfig()
+} catch {
+    print("Failed to load config: \(error)")
+}
+```
+
+#### Security
+- Use Keychain for sensitive data
+- Validate all user input
+- Use App Transport Security (HTTPS)
+- Never hardcode secrets