A builder's clone has its dependencies installed before the run starts, so the type check always has its types

Two pulls this week said tsc failed with "Cannot find type definition file for 'bun'" because the run skipped bun install.

Done:

[ ] When the forge prepares a crew workdir for a repository with a package.json and a lockfile, it installs dependencies from the shared cache (offline-first) before the agent starts; a failure is logged and the run still starts.
[ ] A workdir that already has node_modules for the same lockfile hash is not reinstalled.
[ ] Test: a prepared workdir for a fixture with a lockfile has node_modules; a second preparation does not run install again (count through an injected runner).

Files: src/crew/workdir.ts, its test.

A builder's clone has its dependencies installed before the run starts, so the type check always has its types #6572