Proposal: Add review stage to architecture.md

What

Update the Feature Request System description to include the review stage.

The feature lifecycle now includes a review stage between in-progress and done. Architecture docs should reflect the current system.

Replace:

Feature requests move through: ideas → new → planned → in-progress → done.

With:

Feature requests move through: ideas → new → planned → in-progress → review → done.

Only vault/00_system/docs/architecture.md is affected. Single line change.