[P5][MESH-02] Device authority and remote/home workers

Programme: #1
Epic: #31

## Objective
Allow tasks to run on a selected home/remote device while keeping execution location, transferred context and risky-operation authority explicit and partition-safe.

## Scope
- Worker/device capability advertisement and health.
- Explicit execution placement policy based on device availability, local model/hardware, data locality and grants.
- Scoped encrypted context/artifact transfer to the chosen worker.
- Operation leases/fencing tokens valid across devices.
- Single authority/reservation coordination for risky external commits.
- Partition/offline behavior and stale-worker result rejection.
- Remote worker revocation, key rotation and task migration/recovery.
- User-visible “where this ran / what left this device” trace.

## Correctness rules
- Two devices must not independently commit the same risky operation.
- Late output from a partitioned/old worker cannot acquire fresh authority automatically.
- Remote execution never implies broader data access than local execution.

## Acceptance criteria
- [ ] Concurrent-device fixture proves one risky commit authority at a time.
- [ ] Fencing rejects stale worker dispatch/results after lease replacement.
- [ ] Transferred context is limited to the task's grants and visible in audit UI.
- [ ] Device revocation terminates future task placement/authority.
- [ ] Offline/partition recovery does not duplicate transactions.
- [ ] User can identify whether work ran locally, on a home machine or another authorized worker.

## Dependencies
- MESH-01
- AUTO-01
- TX-02

**First phase:** P5
**Maturity target:** P6
**Owner:** platform

No files, tests, or entry points are named. Start by reading the dependent issues MESH-01, AUTO-01, and TX-02, then map the existing worker, authority, transfer, and audit components. Done means all listed acceptance criteria pass, including fencing, revocation, partition recovery, scoped transfer, and execution-location visibility.

Written by the indexing model from the issue text.