docs: convert pipeline + architecture diagrams to D2, fix storage model and counts

[MrStarktastic]

Summary

• Convert two profile diagrams from Mermaid to D2, rendered to committed light/dark PNGs via <picture>:
  • The Pipeline — the marquee Packer → Terraform → Ansible → Apps flow.
  • Architecture Overview — major revamp with a corrected storage model: TrueNAS as a distinct NFS VM (HBA passthrough, 10.9.8.30 on the services VLAN) serving PersistentVolumes via nfs-provisioner; ZFS pools (8×14TB → 2× RAIDz1); the 1TB NVMe as L2ARC + incomplete-storage cache; separate NVMe os_storage for VM/OS disks.
• Align the Hardware table prose with the corrected storage model.
• Fix stale counts: 17 → 18 workflows; Apps (3) → (4) with the image-scan workflow + Trivy → GitHub Security note.
• Add render tooling (scripts/render-diagrams.sh, .github/.github/workflows/diagrams.yml) + vendored icons with provenance.

Test Plan

• bash scripts/render-diagrams.sh --check exits 0
• Both <picture> images display in light and dark mode on the org profile
• Workflow counts add up (Packer 5 + Terraform 4 + Ansible 5 + Apps 4 = 18)
• Architecture diagram and Hardware table tell the same storage story

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com