Add unified Beacon lookup MCP tool

[Asti1982]

Summary

• add agentfolio_beacon_lookup(beacon_id) as the unified Beacon + AgentFolio SATP MCP endpoint requested in [BOUNTY: 67 RTC] AgentFolio ↔ Beacon Integration Spec + Reference Implementation Scottcjn/rustchain-bounties#2890
• query the live Beacon directory at https://bottube.ai/api/beacon/directory and match AgentFolio SATP profiles via /api/agents and /api/profiles
• return structured statuses for found, partial, not_found, offline, expired/untrusted identities instead of failing the MCP call
• document the new tool and add a mocked regression test for success, missing Beacon, and offline Beacon cases

Proof

• npm test
• live smoke check: unifiedBeaconLookup({ beacon_id: bcn_0x0a_a8f574df }) returns partial with Beacon provenance and SATP warnings

Bounty context

This targets the still-open unified MCP endpoint deliverable from Scottcjn/rustchain-bounties#2890.

RTC wallet for bounty payment: RTCfc0b72ca793ea72a2ba593e7d918d786e4350364

[Asti1982]

Status refresh for this still-open #2890 endpoint PR.

Current contributor-side status:

• PR is open, non-draft, and GitHub reports it mergeable.
• Scope is small: README.md, src/index.js, and test/test.js.
• It adds the requested agentfolio_beacon_lookup(beacon_id) MCP tool with Beacon directory lookup, AgentFolio SATP profile matching, graceful partial/offline/not_found handling, README docs, and mocked regression coverage.
• Original validation in the PR body: npm test; live smoke returned a structured partial result for bcn_0x0a_a8f574df rather than failing the MCP call.

This is intended as the unified MCP endpoint portion of Scottcjn/rustchain-bounties#2890. Happy to make a narrow maintainer-requested adjustment if anything is blocking merge/review.