fix(db): make workspace entrypoint directly importable

[M3stark]

/claim #2775

Summary

• add explicit package metadata for @freelanceflow/db
• provide runtime entrypoints for both ESM and CommonJS consumers
• add a focused import test proving the package resolves by workspace name

Validation

• node -e "import('@freelanceflow/db')"
• node -e "require('@freelanceflow/db')"
• node --test packages/db/test/import.test.mjs
• git diff --check

Payout wallet: 0x8f94Eb732F5044dee8C23ECe9A1BDd801288dfc8