Add Agent Guild endpoint observation tool

[AgentTanuki]

Adds an optional Atomic Forge tool for observing a public agent endpoint selected by the caller before the host connects or delegates. It makes one free request to Agent Guild's hosted /preflight endpoint, which receives and actively probes that URL. The typed result preserves all six check statuses, failed and unknown checks, the exact target, and timing/provenance fields. Contradictory or incomplete responses become typed errors; arbitrary service prose is omitted. The host retains control over any subsequent action.

The contribution includes synchronous and asynchronous interfaces, optional exact host restrictions, bounded response handling, examples, tests, a Forge index entry and the workspace lockfile update. It requires no Guild account, API key or payment. Atomic Assembler's actual discovery/copy functions are exercised, including the copied tool's import after packaging metadata is excluded.

Validation against Atomic Agents 2.10.2 at 33d2ec94f42d4a65393a336e35edf21ee5700303:

• 58 tool tests passed using real Atomic classes, real agent/schema composition and real HTTPX clients with the provider/HTTP boundaries substituted.
• 339 core tests passed; 3 skipped.
• Black checked all 203 Python files; Flake8 passed.
• The generated lockfile adds the new workspace member without changing existing dependency versions.

Tests make no live model or Guild request. The retained response fixture is a first-party observation from September 11, not evidence of outside adoption. A successful observation is not identity, safety or execution authorization.