v0.2.2 — MAT- prefix enforced; all examples updated to v0.2.0

Fixed

• MaterialDNA `id` pattern now requires `MAT-` prefix (`^MAT-[A-Z]{2}-[A-Z]{3}-\d{4}-[A-Z]+-[A-Z0-9]{6,}$`) — consistent with spec and symmetric with ProductDNA's `PRD-` prefix
• Updated schemas: `offer`, `match`, `transfer`, `material-status`, `transaction`, `loopcoin`, `product-dna` — all `material_id` / `material_ref` / `material_ids` patterns now require `MAT-` prefix
• All 15 example payloads updated: `schema_version: "0.2.0"`, `@context: loop-v0.2.0.jsonld`, and MaterialDNA ID fields prefixed with `MAT-`

Changed

• `SPECIFICATION.md` §3.6 added: entity status-transition reference table (Offer, Match, Transfer, MaterialStatusUpdate, Transaction)