Key changes from v1:
- Drop 3-instance replication → 2-instance CNPG, single Redis/MySQL
- Remove Headscale from PG migration (project discourages it)
- Remove MeshCentral from PG migration (NeDB, not SQLite)
- Replace Redis Sentinel with single redis:7 on local disk (modules unused)
- Add RAM overcommit warning and mitigation
- Add explicit single-host limitation acknowledgment
- Add per-component rollback plans
- Fix backup strategy (CNPG can't archive WAL to NFS natively)
- Reorder migration: low-risk services first, authentik last
- Add research gate before each service migration
