[Architecture] Hub federation mode — cross-repo lesson sync

[Ikalus1988]

Task

Implement Hub federation: a Hub node aggregates lessons from multiple repos and serves unified search.

Acceptance Criteria

• Hub node can pull lessons from registered Node repos
• Conflict resolution: latest timestamp wins, quality score breaks ties
• Auth: HMAC-signed requests between Hub and Nodes
• Incremental sync: only changed lessons transferred
• Dashboard: Hub shows connected Nodes + lesson count per Node

Why it matters

Federation is the core vision — one agent's lesson benefits all agents.

Difficulty

🔴 Ring-4 — distributed system architecture.

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