Add optional MCP extension with durable jobs and monitoring

[promisingcoder]

Summary

Add an optional local stdio MCP extension, with all implementation, tests and extension documentation under mcp/.

• Expose advertiser discovery, searches, native pagination, enrichment, full supplied Meta records, media, local filtering, exports, reports, events, private proxy profiles and explicit webhooks.
• Add transactional SQLite results, background jobs, page checkpoints, crash recovery, process leases and durable monitoring schedules.
• Add an explicitly started persistent worker for operation independently of an AI client.
• Keep core Python source unchanged. Outside mcp/, change only packaging metadata, source archive inclusion and CI wiring.
• Keep the MCP SDK optional; the ordinary collector installation has no SDK dependency.

Verification

• 133 MCP checks passed on the final revision: 122 infrastructure/regression tests and 11 actual Meta tests, with zero failures or skips in the selected suites.
• Actual SDK stdio initialization, typed tools, resource reads and lifecycle verified.
• Real Meta pagination, exports, enrichment, media, monitoring and worker process-kill recovery verified.
• Installed wheel tested outside the checkout, including plain installation without the SDK and installation with the optional extra.
• Core regression suite passed (909 passes; 3 existing optional/environment checks skipped locally).
• All 21 core files in the GitHub-built wheel are byte-for-byte identical to the public PyPI 1.5.1 wheel.
• Final tracked changes, GitHub-built wheel and source archive scanned against private credentials; no matches.
• All 19 jobs in final CI succeeded at commit 49573e5bee4c7c30ef5d5d47bd24181cb0d3ed8a, including Python 3.10–3.14 and Windows MCP coverage, existing core matrices, clean installed-wheel checks and both live Meta suites.
• Independently tested the exact GitHub-built wheel against real Meta with the minimum supported curl_cffi==0.13.0: all 11 live tests passed.

The existing PyPI release remains unchanged. This PR adds the implementation and packaging support for a future release of the extra.