reports: make DB discovery source-agnostic

Bogdan Tsechoevrequested to merge
fix/reports-db-discovery-and-bloat-filtering into main
  • Refactor get_all_databases() to unify DB names from multiple sources:
    • pgwatch_pg_database_wraparound_* (datname)
    • unused/redundant indexes (dbname)
    • pg_btree_bloat metrics (datname)
  • F005 report:
    • Align with dashboards by excluding entries with bloat_pct <= 0
    • Clamp negative extra_/bloat_ values to zero

This prevents empty/zero F005 results due to label mismatches and removes spurious negative bloat artifacts from the report output.

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