Implement generated artefact persistence, manifest preview, and repository-friendly export workflow

[kalen-releasedgroup]

Summary

Make generated output reviewable and exportable as a first-class product workflow.

Scope

• Persist generated artefact bundles and manifest records.
• Implement code preview with file list/manifest view.
• Support repository-friendly export layout for committing output elsewhere.

Requirement Links

• FR-GEN-006, FR-GEN-009
• Sections 9.4, 10.3

Dependencies

• Generated output pipeline
• Artefact storage abstraction

Exit Criteria

• Generated artefacts are stored and traceable.
• Users can inspect the manifest and code preview in the UI.
• Export produces a stable, repository-friendly file layout.