fix: set PD_MONGO_URI for in-cluster mongo and enable in_cluster (#145)

Co-authored-by: Junyi Hou <junyi@xtras3.tail08d22c.ts.net>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
fix as #143/#144 (development) and #140 (main).

Author: 3 people