WA-PERF-001: Dragonfly → libvips migration plan + Content::Asset prototype

[kitcommerce]

Summary

Addresses #703 — research and prototype for replacing Dragonfly with a lightweight libvips-based storage layer.

What's included

Migration plan (docs/notes/dragonfly-migration-plan.md)

• Full audit of all Dragonfly usage across the codebase (14+ models, custom processors, freedom patches, routing)
• ActiveStorage vs direct libvips comparison (ActiveStorage lacks Mongoid support — not viable)
• Recommended approach: custom storage layer + libvips processing
• Backward compatibility strategy for downstream users with custom Dragonfly processors
• Phased migration timeline and risk assessment

Prototype: Content::Asset behind a feature flag

Enable with WORKAREA_MEDIA_BACKEND=media_v2 (off by default — zero impact on existing behavior).

• Workarea::Media::Storage — S3/filesystem storage using existing Workarea.config.asset_store
• Workarea::Media::Attachment — Dragonfly-compatible wrapper (.url, .optim.url, .process())
• Workarea::MediaController + /media2/ route (avoids Dragonfly middleware collision)
• Content::Asset swaps backends at runtime when flag is enabled

What's NOT included (documented for follow-up phases)

• Migration of other Dragonfly consumers (ProductImage, Avatar, Sitemap, etc.)
• URL compatibility layer (Dragonfly URLs → new URLs)
• CSV import/export path updates
• Custom processor migration guide for downstream users

Client impact

None when flag is off. When enabled, only Content::Asset is affected. Full migration will need a deprecation period.

Testing

Prototype phase — manual verification. Automated test coverage planned for subsequent phases.

Closes #703