feat: Add google flight search tool

[meirk-brd]

Suammary

A new flight_search tool that retrieves comprehensive flight information from Google Flights SERP. The tool accepts origin, destination, and optional travel dates, returning structured flight data including carrier info, duration, pricing, date-based price ranges, and detailed flight options (markdown) descriptions.

Response Structure:

{
  "origin": "string",
  "destination": "string", 
  "date_from": "string|null",
  "date_to": "string|null",
  "options": [/* flight items with carrier, duration, price, link */],
  "price_ranges": [/* date-based price variations */],
  "detailed_results": [/* markdown descriptions of each flight */]
}