Add client hints and DuckDuckGo detection

[jonathanKingston]

Adds User-Agent Client Hints support with DuckDuckGo browser detection.

• Parses Sec-CH-UA-* headers into structured ClientHints object (brands, mobile, platform, etc.)
• Detects DuckDuckGo browser via two methods:
  • Chromium platforms (Android, Windows): "DuckDuckGo" brand in Sec-CH-UA
  • WebKit platforms (iOS, macOS): Ddg/X.Y.Z suffix in UA string
• New isDuckDuckGo flag and clientHints property on AgentDetails
• Express middleware automatically parses client hints when present
• Exports new types: ClientHints, ClientHintBrand

[biggora]

@jonathanKingston
The code processes external HTTP headers without adequate error handling, creating multiple vectors for application crashes.

1. Add error handling to all parseClientHints() helper functions with try-catch blocks
2. Add input validation - length limits, type checks, iteration limits
3. Add DuckDuckGo to browsers object for consistency with existing pattern
4. Fix line endings - run npm run lint:fix
5. Add test for DuckDuckGo in fullVersionList only (currently untested code path)

[jonathanKingston]

Hey @biggora thanks for the feedback, I think I've addressed it all. Let me know if there's further concerns.