Expose provider reclamation window in provider status endpoint

[linear]

Why

The provider already supports a configurable reclamation window (--reclamation-window) and includes it in the bids it creates. The provider status endpoint does not expose it, so provider inventory and bid-screening clients cannot tell whether a provider offers reclamation before screening or bidding.

What

Expose the configured reclamation window in provider status. A missing value means the provider does not offer reclamation.

Flows that should work:

1. Provider inventory clients reading provider status see the reclamation window when one is configured.
2. Bid-screening clients consuming provider status (REST and gRPC) can use the reclamation window to screen providers before bidding.

Acceptance Criteria

• Provider status (REST and gRPC, including streaming) reports the configured reclamation window, and omits it when not configured.
• Existing bid behavior is unchanged.