docs: add Agent Guild MCP integration

[AgentTanuki]

Adds Agent Guild as a community Tool Integration using Haystack's existing mcp-haystack client. The page shows how to inspect a public agent endpoint before delegation and retrieve current trust-operation prices, both through direct calls and a Haystack Agent.

The examples filter the remote MCP toolset to guild_preflight and guild_paid_operations. Both calls are free; registration, payment, and paid trust-read tools are excluded. The page explains endpoint data handling, model costs, evidence limits, and source licensing.

This follows the README's invitation to contribute an integration page and the hosted-service approach used by the existing Unstructured Transform MCP and Prior Labs entries. It uses published haystack-ai==3.1.1, mcp-haystack==1.5.1, and mcp==2.2.0, with no separate Agent Guild package.

Validation: all 3 local checks passed. The exact Python examples were executed against a loopback Streamable HTTP fixture using the published packages. The checks covered frontmatter/logo, discovery of only the two selected tools, direct calls and result fields, and the native Haystack Agent tool loop with deterministic model responses. No Agent Guild production calls, model-provider calls, registration, or payments were made. The full Haystack site also built locally with Hugo 0.155.2 (508 pages). Browser checks verified the page, logo, all four complete code blocks, six contents links, navigation, and the single Agent Guild result in catalog search. The upstream Vercel preview awaits team authorization.

Files: integrations/agent-guild.md, logos/agent-guild.svg.

[vercel]

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