Add keeperhub directory to migrator Docker stage

[eskp]

Problem

The db-migration init pod fails with:

Error: Cannot find module '../../keeperhub/db/schema-extensions'

The migrator stage in the Dockerfile wasn't copying the keeperhub/ directory which contains schema-extensions.ts.

Fix

Dockerfile

  COPY --from=builder /app/lib ./lib
+ COPY --from=builder /app/keeperhub ./keeperhub
  COPY --from=builder /app/package.json ./package.json

Test Plan

• Deploy to staging and verify db-migration pod succeeds