v0.3.0

Added

• Added a top-level, non-mutating diff command for inspecting a recorded
  upstream commit change, with capped human output, --verbose, and a stable
  --json schema containing complete path groups.

Changed

• The README is now a concise installation and everyday-workflow entry point;
  detailed archive operations, configuration/storage, and experimental torrent
  guidance moved into focused documents under docs/.
• Added a repository-wide agent contract and consolidated detailed development
  guidance in the conventional CONTRIBUTING.md.

Fixed

• Failed first-time mirrors now resolve and validate the upstream snapshot
  before creating an archive entry. Misspelled, inaccessible, and invalid
  repositories no longer leave an empty in_progress mirror behind, while
  failures after a commit-pinned download begins remain explicitly resumable.
• Mirror failures now print a concise categorized result and exact retry or
  resume command instead of exposing an uncaught traceback for expected Hub and
  transport errors.