Expand description
Port for persisting TechnicalSpec and TechnicalSpecSignature
entities (Story 3.8 — FR33).
All methods return Result<_, AppError> natively — no legacy String
error debt to migrate later (CRITICAL.md #4 / #555).
Signatures are append-only — the repository exposes only save_signature
and a few read methods; mutation guards are enforced at the DB trigger
level (cf. migration 20260605060000_create_technical_specs.sql).