SnapshotAnalyzer

Records an architecture as a committable snapshot, and compares two of them.

A branch can change the dependency graph without that being visible in the diff. Committing a snapshot and comparing against it makes the change reviewable - "this pull request adds a dependency from the domain layer to the UI layer" becomes a line in the review.

The snapshot is small and sorted so it diffs line by line, and both functions are pure: the same graph always produces the same file, and the same pair always produces the same report.