PostgresStore was 86% stubs behind a build tag nothing enables, pgdbgen
carried hand-added build tags that fought sqlc-verify, and the runtime never
threaded store.Store through the handler boundary. Single-engine reality
shrinks the W1-3 attachment-ownership fix and ends the pgdbgen churn.
Removed: store/postgres.go, db/pgdbgen/, db/queries/postgres/,
migrations/postgres/, the sqlc postgres block, pgx from go.mod, the
startup-refusal branch, and the dead Postgres config surface.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>