Retry transient workspace install failures - #57

Summary

Make repository-wide dependency installation resilient to transient runner filesystem races such as ETXTBSY from freshly installed native binaries.

Changes

• replace the brittle chained npm ci command with scripts/install-all.mjs;
• install backend, frontend, and website independently;
• retry a failed workspace up to three times with bounded backoff;
• remove only the failed workspace's node_modules before retrying;
• preserve a hard failure after the retry budget is exhausted.

Safety

Lockfiles remain authoritative because every attempt still uses npm ci. No dependency versions, application code, workflow permissions, deployment settings, or merge gates are changed.