Remove the default embedding package from the chromadb dev dependencies

[cristianrgreco]

Summary

Removes @chroma-core/default-embed from the chromadb module's dev dependencies. That takes onnxruntime-node out of the install, which is what broke Lint on main.

• packages/modules/chromadb/package.json: the dev dependency is removed. The lockfile loses 55 packages (@chroma-core/*, @huggingface/transformers, onnxruntime-node, onnxruntime-web, sharp and its platform packages) and nothing else changes.
• docs/modules/chromadb.md: the package is now listed as optional for the examples, with what happens without it.
• An earlier commit on this branch set ONNXRUNTIME_NODE_INSTALL_CUDA=skip in the npm-setup action. With the package gone that's no longer needed, so the action is unchanged from main.

Why

The Lint job failed on main after #1495 (run). It wasn't a lint error. npm ci failed:

npm error path .../node_modules/onnxruntime-node
npm error command sh -c node ./script/install
npm error Downloading "https://github.com/microsoft/onnxruntime/releases/download/v1.21.0/onnxruntime-linux-x64-gpu-1.21.0.tgz"...
npm error Error: Failed to download the binaries: 504 Gateway Time-out.

onnxruntime-node came in through @chroma-core/default-embed. On Linux x64 its postinstall script downloads a 214 MB archive of CUDA libraries from GitHub. Since #1495 every job installs every workspace, so when the shared cache is missing, a failed download fails whichever job hits it. The same error also failed a test job on #1492.

The chromadb tests don't need the package. They pass embeddings explicitly or supply their own embedding function. Without it, chromadb logs a warning when a collection has no embedding function and carries on.

Verification

• The chromadb suite was run in a copy of the repository outside the checkout, installed without the package, where require.resolve("@chroma-core/default-embed") fails: 5 of 5 tests pass, including the Ollama embedding test. chromadb logged its "Please install @chroma-core/default-embed" warning 12 times.
• npm ci succeeds with the new lockfile and leaves it unchanged. The lockfile diff is the 55 removed packages plus the workspace's manifest entry.
• npm run format, npm run lint, npm run check-compiles: pass.

Effect on installs

• Local node_modules goes from 1.3 GB to 934 MB.
• The shared CI cache was 445 MB with the CUDA libraries and 280 MB with the download skipped. It should be smaller again without these packages; this PR's CI run will show the figure.

Follow-up for #1492

#1492's knip.jsonc ignores @chroma-core/default-embed for the chromadb workspace. Once this is merged that entry is unneeded; knip will print a configuration hint for it until it's removed.

Why this isn't breaking

@chroma-core/default-embed was a dev dependency, so @testcontainers/chromadb's published dependencies don't change. No package source changes.