docs: align architecture guides with implementation

[sbalabanov]

Summary

Intent:

• Keep the repository's canonical architecture guidance consistent with the current service and pipeline boundaries.
• Distinguish durable snapshots, request-log projections, and queue wire formats accurately.

Changes:

• Updated AGENTS.md and domain overviews for current controller, storage, queue, and Stovepipe behavior.
• Corrected Gateway and Orchestrator lifecycle documentation and refreshed extension-specific guides.

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Generated by the pr-create skill in devexp-agent-marketplace.

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