Add native web search for providers with server-managed search tools.

Why not use brave-search skill? Native tools = model decides when to search, auto-citations, no extra API key, server-side execution.

agents:
  defaults:
    webSearch:
      enabled: true
      maxUses: 5
      allowedDomains: []
      blockedDomains: []
      userLocation:
        country: ""
        city: ""

{ "type": "web_search_20250305", "name": "web_search", "max_uses": 5 }

model="gpt-4o-search-preview", web_search_options={}

{ "type": "web_search" }

tools=[{"google_search": {}}]

Upstream: badlogic/pi-mono#709