Implement DB Reconnection in Java Client and Startup Recovery on Initial Connection Failure

[panzer-punk]

The Java client currently fails on a clean startup if the database is unavailable at service start.
We need to add resilience for database connectivity in two scenarios:

1. Runtime disconnect — automatically recover the DB connection when it is lost during normal operation.
2. Startup failure — if DB is unavailable on startup, the service should either:
   • keep retrying connection with backoff until success, or
   • restart gracefully (based on agreed operational strategy).