Implement authenticated debug-console sessions

[Hrabovszki1023]

Summary

• authenticate the Pylontech console with login <credential> and require the exact pylon_debug> prompt before polling
• re-verify and re-authenticate after transport reconnects, with bounded reconnect recovery from Reconnect Waveshare transport automatically after persistent acquisition failure #42
• fail closed when authentication is rejected or the console leaves debug mode
• attempt logout on controlled shutdown
• expose sanitized session mode/authentication health through REST and the read-only web status area
• support mutually exclusive password or password-file configuration and document Docker Secret plus isolated-network deployment

Why

pwrsys is only available in the authenticated debug console. Without an explicit session lifecycle, rack acquisition repeatedly fails while other read-only commands may still work.

Validation

• PYTHONPATH=src python -m pytest — 231 passed
• python -m ruff check . — passed
• python -m mypy src tests — passed
• git diff --check — passed

Docker is not installed in the local Windows workspace, so Compose/build and real Waveshare hardware verification remain for the Docker server before merge.

Closes #48