feat(shell): add persistent virtual workspace

[cekrauseee]

Summary

• Replace the chat path with a persistent just-bash virtual workspace backed by anonymous sessions and PostgreSQL.
• Add resilient terminal behavior: persistent history, inline command output, explicit unsupported-command errors, classic Enter handling, and Ctrl+C interruption feedback.
• Add focused component and filesystem tests plus local setup and developer documentation.

Validation

• npm run format:check
• npm run lint
• npm run typecheck
• npm run test:run (22 tests)
• npm run build