Add deerflow.community.serply.tools:web_search_tool, a Google SERP
provider for the web_search slot that also covers Google News and Google
Scholar through an optional `vertical` config option. Reads the key from
api_key in config.yaml or SERPLY_API_KEY, clamps max_results to Serply's
1-100 range, and returns the same structured JSON errors as the Serper
and Brave tools.
Register the provider in config.example.yaml, scripts/doctor.py,
scripts/wizard/providers.py, .env.example, backend/docs/CONFIGURATION.md,
the en/zh tools.mdx provider tabs, and tools/AGENTS.md. Tests mock httpx.
