Steal Tasks

Evaluate task stealing policy and reassign claimed tasks between nodes.

Workers report their queue depths; the server runs the steal policy and returns a list of task reassignments. Stolen tasks are reset to open so the receiver node can claim them.

Authorisation requires the node-admin scope, like the other node-registry mutations (cordon, uncordon, drain, unregister) this sits beside in the operational-primitives table. It is deliberately NOT the heartbeat scope that POST /cluster/claims/gossip uses: gossip proves each receipt with its own Ed25519 signature and chain link inside the handler, so its bearer scope only has to establish fleet membership, whereas here the caller's reported queue depths drive force_claim directly with no further proof to check.