Document Paperless Tika/Gotenberg sidecars, supported Office/OpenDocument ingestion formats, stack paths, validation/deploy procedure, and verification commands. Updates service inventory and architecture overview so PD docs match the deployed documents stack.
- docs/README.md: add full documentation index (was empty)
- docs/servers/ROCINANTE.md: create new server doc (RTX 4090, heavy inference)
- docs/servers/SERENITY.md: fix CPU spec (dual X5690, not single); add reranker service
- docs/architecture/SERVICES_DIRECTORY.md: fill in all service ports (was all dashes)
- docs/architecture/ARCHITECTURE_OVERVIEW.md: mark all services as deployed
- docs/planning/HOMELAB_EXPANSION_PLAN.md: mark all 6 phases complete
