Preview seed fixture (rolling)

Rolling, fully SYNTHETIC preview-database seed fixture baked from dev@01b630f8fc7d (migration head: 20260802120000_add_capability_cards_step). Preview environments restore fixture.dump.gz (custom-format, gzipped, platform schema only, including _prisma_migrations) BEFORE running a PR's own migrations, so schema changes run against populated tables. RESTORE: apply restore-preamble.sql to the target database first (it creates the platform schema and installs the vector + pg_trgm extensions into it, which pg_dump --schema=platform omits), then run 'gunzip -c fixture.dump.gz | pg_restore -d --no-owner' WITHOUT --exit-on-error (the dump's own CREATE SCHEMA collides benignly with the preamble's). SECURITY INVARIANT: this bake holds no cloud credentials and has no read path to any real database — it runs entirely against a throwaway Postgres container and contains only Faker-generated synthetic rows plus the already-public marketplace agent exports checked into autogpt_platform/backend/agents/. This asset is regenerated on every eligible dev push and weekly; treat it as disposable.