[E6-2] Dedicated-synchronizer Scan endpoints (funding side only)

[salindne]

New endpoints: list registered synchronizers; per-sync purchased/burned totals; serve the RegisteredSynchronizer disclosed contract a buyer attaches. Omit total_consumed (separate endpoint, not reusing getMemberTrafficStatus's shape) - consumption visibility is the operator's choice.

Key files: apps/scan/.../store/ScanStore.scala:382, scan.yaml, apps/scan/.../HttpScanHandler.scala

Acceptance criteria:

• A buyer can fetch the operator party + disclosed registration from Scan
• Endpoints expose funding totals; no consumed field

Depends on: E6-1

Epic: #9

Source: docs/planning/extending-mainnet-work-plan.md