test: implement RPR_MEND_DB teardown after RPR_VALIDATE_DB in fbird_service_db_mgr.phpt

[satwareAG-ironMike]

Problem

fbird_service_db_mgr.phpt calls fbird_maintain_db($service, $db_path, FBIRD_RPR_VALIDATE_DB, FBIRD_RPR_FULL) but never follows with FBIRD_RPR_MEND_DB. Per .clinerules: RPR_VALIDATE_DB leaves a stale "damaged" flag that causes subsequent backup tests to fail with checksum errors.

Fix

Add fbird_maintain_db($service, $db_path, FBIRD_RPR_MEND_DB, FBIRD_RPR_FULL) as teardown after validate.

Source

QA Audit 2026-04-09 - Finding T5 (Priority P2/P3)