docs: add docs directory info and nixos options improvement plan

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -125,6 +125,9 @@ This ensures documentation matches the exact nixpkgs version (currently NixOS 25
   - `http-proxy/`, `ca/`, `postgres/`, `nats/`, `jellyfin/`, etc.
 - `/secrets/` - SOPS-encrypted secrets with age encryption
 - `/common/` - Shared configurations (e.g., VM guest agent)
+- `/docs/` - Documentation and plans
+  - `plans/` - Future plans and proposals
+  - `plans/completed/` - Completed plans (moved here when done)
 - `/playbooks/` - Ansible playbooks for fleet management
 - `/.sops.yaml` - SOPS configuration with age keys for all servers