B-1: Module-split cleanup for 8 files >500 LOC (charter Pillar 1 Major)

[mphacker]

Phase 5 close-out charter-review backfill (commit cdcb38c) flagged 8 Python source files exceeding the charter's 500-LOC hard ceiling. All are gates-clean and shipped through automated CI, but the charter calls for a refactor split:

• services/mapping_queries.py — 1492 LOC (split per-domain query module)
• services/mapping_migrations.py — 875 LOC (split per-schema-version)
• blueprints/mapping.py — 1015 LOC (split routes by tab)
• services/cloud_oauth_service.py — 764 LOC
• services/cloud_rclone_service.py — 926 LOC
• blueprints/cloud_archive.py — 905 LOC
• services/samba_service.py — 563 LOC
• services/cleanup/service.py — 673 LOC

Reference: docs/charter-reviews/charter-review-5.{13,14,15,16,17,18}.md. Recommended for a dedicated cleanup phase between Phase 5 close and Phase 6 setup.sh work — split-PRs only, no behaviour change.