Fix Finance database network resolution

[iPior]

Summary

• remove the obsolete finlens_private network from the API service
• remove the obsolete finlens_private network from the MCP server
• remove the external finlens_private network declaration
• keep pior_data as the shared database network

Why

Finance was resolving the database hostname postgres to the legacy shared-postgres container on finlens_private (172.23.0.2) instead of the platform-managed pior-postgres container on pior_data (172.24.0.2). This caused the migration to fail with PostgreSQL 28P01 even though the finance_app credentials were correct.

A migration run with the database hostname temporarily overridden to pior-postgres succeeded, confirming the network/DNS collision as the root cause.