docs: match the Docker Swarm stack's ChromaDB server to the client the image ships and fix its Ollama and secret key settings

[silentoplayz]

Summary

I compared the Docker Swarm stack on both Swarm pages (the quick-start tab and the deployment guide) with what the Open WebUI image needs and with the Chroma 1.5.9 image.

• ChromaDB: the stack pinned a Chroma v0.5.15 server while the Open WebUI image ships the chromadb==1.5.9 client, which only speaks the v2 API. The image is now pinned to v1.5.9 and its data path moved to /data, which is where the v1 image's chroma run /config.yaml persists. The IS_PERSISTENT, ALLOW_RESET and PERSIST_DIRECTORY variables of the old image are dropped. The curl healthcheck is removed because the v1 runner image installs no curl.
• OLLAMA_BASE_URLS became OLLAMA_BASE_URL. With only the plural set, the image's default /ollama is rewritten to http://host.docker.internal:11434. That rewritten value is what RAG_OLLAMA_BASE_URL inherits. The Ollama embedding engine therefore pointed at a host that does not exist inside the stack.
• The tab page's stack set no WEBUI_SECRET_KEY, so every task recreation signed everyone out. The deployment page already had it.
• WEBUI_NAME is displayed with an " (Open WebUI)" suffix, now noted on the example value.

Related issue or discussion

None.

Checklist

• I have reviewed the relevant documentation and matched the existing style.
• This PR meets Open WebUI's contribution standards: it is accurate, relevant to users, narrowly scoped, maintainable, and not promotional content, advertising, lead generation, SEO placement, or a request to list a product, service, provider, integration, gateway, tool, or company primarily for visibility.
• I understand that PRs that do not meet these standards may be closed without review and will not be merged. Repeated, low-quality, off-topic, promotional, or intentionally misleading submissions may result in the contributor being blocked from future participation in Open WebUI repositories.

Notes for reviewers

Sources on dev: backend/requirements.txt for the chromadb pin, retrieval/vector/dbs/chroma.py, config.py for the Ollama URL rewrite and RAG_OLLAMA_BASE_URL, env.py for WEBUI_NAME, and backend/start.sh for the secret key file. For the Chroma side, I read the v1.5.9 image config from the Docker Hub registry (entrypoint dumb-init -- chroma, command run /config.yaml), and rust/Dockerfile plus docker_single_node.yaml at the v1.5.9 tag of chroma-core/chroma. I have not deployed the stack.