docs: drop stale chromadb-setup.md; strip broken VM-102 frontmatter

Second pass on docs/ cleanup (item #15 in STATUS.md):

- pfi/chromadb-setup.md: deleted. References configs/pfi-ana/... and
  scripts/setup-chromadb.sh, neither of which exist in this repo
  (artifacts of an earlier project layout). ChromaDB is already live
  per docker-stack.md; the operational truth lives there.
- pfi/docker-stack.md: removed the cross-link to the deleted file and
  pulled the bit of useful content from it (auth-token generation +
  client Settings example) into the inline ChromaDB section.
- pfi/vm-102-matrix-{synapse,appservice}.md: stripped the YAML
  frontmatter. The `path:` values pointed at docs/pfi-ana/... which
  doesn't exist in this repo; no toolchain consumed the metadata.
- README.md: tree updated to reflect the deletion.

VM-102 docs kept separate by design — each is right-sized; merging
would push past the ~500-line guideline.

docs/README.md

@@ -14,7 +14,6 @@ docs/
 │   ├── disaster-recovery.md
 │   └── pbs-deployment.md
 └── pfi/                      # PFI-specific reference (services, models, VMs)
-    ├── chromadb-setup.md
     ├── docker-stack.md
     ├── model-list.md
     ├── proxmox-vms.md