Add comprehensive API documentation for ConfigKeyKit, MistDemoConfig, and AuthenticationHelper

[leogdion]

While some inline comments exist, many public APIs lack proper documentation. This makes it harder for developers to understand and use the configuration system.

Missing Documentation

1. ConfigKeyKit Library

• ConfigurationKey protocol - purpose and usage
• NamingStyle protocol - when to implement custom styles
• ConfigKey<T> - required vs optional config distinction
• OptionalConfigKey<T> - when to use vs ConfigKey
• StandardNamingStyle - transformation examples

2. MistDemoConfig

• EnhancedConfigurationReader - hierarchy and resolution order
• Public properties - what each config value controls
• Initialization - what sources are consulted
• Error cases - when initialization fails

3. AuthenticationHelper

• AuthenticationResult struct - what each field represents
• setupAuthentication() - decision tree logic
• Database selection rules - which auth methods require which databases
• Error cases - when authentication setup fails

Documentation Style

Use Swift's documentation comment format:

```swift
/// Manages hierarchical configuration resolution from multiple sources.
///
/// Configuration values are resolved in the following order (highest to lowest priority):
/// 1. Command-line arguments (`--key-name value`)
/// 2. Environment variables (`CLOUDKIT_KEY_NAME`)
/// 3. Default values (specified at initialization)
///
/// Example:
/// ```swift
/// let reader = EnhancedConfigurationReader()
/// let apiToken = reader.string(
/// key: "api.token",
/// environmentKey: "CLOUDKIT_API_TOKEN",
/// default: ""
/// )
/// ```
internal struct EnhancedConfigurationReader {
// ...
}
```

Example: ConfigKey Documentation

```swift
/// A type-safe configuration key with a required default value.
///
/// Use `ConfigKey` when a configuration value should always have a sensible default.
/// For optional configuration (like credentials), use `OptionalConfigKey` instead.
///
/// Example:
/// ```swift
/// let containerKey = ConfigKey(
/// "container.identifier",
/// envPrefix: "CLOUDKIT",
/// default: "iCloud.com.example.App"
/// )
/// ```
///
/// This generates:
/// - CLI argument: `--container-identifier`
/// - Environment variable: `CLOUDKIT_CONTAINER_IDENTIFIER`
/// - Default: `"iCloud.com.example.App"`
public struct ConfigKey<Value: Sendable>: ConfigurationKey {
// ...
}
```

Files Needing Documentation

• Examples/BushelCloud/Sources/ConfigKeyKit/ConfigurationKey.swift
• Examples/BushelCloud/Sources/ConfigKeyKit/ConfigKey.swift
• Examples/BushelCloud/Sources/ConfigKeyKit/OptionalConfigKey.swift
• Examples/MistDemo/Sources/MistDemo/Configuration/MistDemoConfig.swift
• Examples/MistDemo/Sources/MistDemo/Utilities/AuthenticationHelper.swift

Acceptance Criteria

• All public types have /// documentation comments
• All public methods have parameter and return value documentation
• Error cases documented with - Throws: sections
• Usage examples included for complex APIs
• Configuration hierarchy documented (CLI > ENV > defaults)
• Authentication decision tree documented
• Database selection rules documented
• Consider adding a CONFIGURATION.md guide

Tools

• Use Xcode's documentation preview (Option+click on symbol)
• Consider generating docs with SwiftDoc or Jazzy

Related Work

• PR description checklist item: "Update README.md with ConfigKeyKit usage"
• Could expand into comprehensive configuration guide

References

• Swift documentation guidelines: Swift API Design Guidelines

[leogdion]

Still needed with updated scope.

With the migration to Swift Configuration (commits d500e0a, 44f4bbf), the components needing documentation have changed:

Components Needing Documentation

1. ConfigKeyKit Module

• ConfigurationKey protocol - purpose and usage
• ConfigKey and OptionalConfigKey types - when to use each
• NamingStyle patterns

2. MistDemoConfiguration

• Swift Configuration integration
• Provider hierarchy (Environment → Defaults)
• Key transformation rules
• Secret handling

3. MistDemoConfig

• Public properties - what each config value controls
• Initialization flow
• Error cases

4. AuthenticationHelper

• Authentication method decision tree
• Database selection rules
• Error conditions

The EnhancedConfigurationReader no longer exists, but the need for comprehensive API documentation remains critical for maintainability.