fix: support mounted .env files in container deployments

[Bushstar]

Summary

• add a shared env loader for MDIP services
• support mounted .env files in containers without requiring a custom entrypoint.sh
• support KC_ENV_FILE for env files mounted at non-default paths
• keep existing ./start-node and direct environment injection behavior unchanged
• document the supported deployment patterns for Docker Compose and Kubernetes

Problem

Local startup works because ./start-node sources the repo root .env and docker compose injects the resolved values into each container.

In standalone container deployments such as Kubernetes, operators may mount a .env file into the container, but the service does not automatically load that file unless they add a wrapper script to source and export it first.

Solution

This PR adds a shared env-loading utility in @mdip/common and updates the runtime services to use it at startup.

The loader now supports the following configuration patterns:

• direct env injection via env / envFrom
• a mounted .env file at /app/.env
• a mounted env file at any path referenced by KC_ENV_FILE

The loader preserves existing behavior by not overriding variables already present in process.env.

• Resolves: Support mounted .env files in container deployments without custom entrypoint scripts #1195