RFC 0017: Epic / Tracking issue for snapshot copy between repositories

[rmanibus]

Context

Track completion and rollout for RFC 0017 (Snapshot Copy Between Repositories).

RFC: rfcs/0017-snapshot-copy-between-repositories.md

Goal

Provide a first-class way to copy snapshots between Cloudstic repositories while preserving snapshot semantics and fitting the existing CLI and client models.

Scope

• cloudstic copy command for repository-to-repository snapshot transfer.
• Source repository configuration and credential handling for copy.
• Snapshot selection by explicit IDs and existing snapshot filters.
• Provenance-aware skip logic for reruns.
• Client API support for Client.Copy(ctx, from, opts...).
• Documentation of copy semantics, bandwidth costs, and dedup expectations.
• Hermetic tests for copy behavior across supported backends.

Explicitly out of scope

• Backend-native server-side clone behavior.
• Guaranteeing identical storage footprint or object naming between source and destination repositories.
• Broader repository migration/refactor work beyond snapshot copy semantics.

Exit criteria

• The main copy workflow described in the RFC is implemented or intentionally descoped.
• Repeated copy runs skip already copied snapshots using explicit provenance tracking.
• Copied snapshots are listable and restorable from the destination repository.
• Docs explain operational costs and limits of repository-to-repository copy.