docs(extraction): move NimClient guide from published docs to developer_docs

[kheiss-uwzoo]

Summary

Follow-up to PR #2257 per Randy's review: the NimClient usage guide is developer-facing content and should not be a formal published extraction page.

• Moved content from docs/docs/extraction/nimclient.md to nemo_retriever/developer_docs/nimclient.md
• Indexed the guide in nemo_retriever/developer_docs/README.md
• Removed the standalone NimClient and custom NIM endpoints nav entry from docs/mkdocs.yml
• Added a redirect from extraction/nimclient.md to the developer docs file for legacy URLs
• Left a one-line crosslink in the graph README pointing to the NimClient guide
• Updated import paths and API guide links in the moved content to match current main module locations

Test plan

• MkDocs build passes
• check-nrl-doc-leakage.ps1 -Base main passes on the branch diff
• Published nav no longer lists a separate NimClient page under 8. Customize & extend
• Legacy /extraction/nimclient/ URLs redirect to nemo_retriever/developer_docs/nimclient.md
• Developer docs index lists NimClient alongside other internal guides

[greptile-apps]

Greptile Summary

This PR relocates the NimClient usage guide from the published MkDocs site (docs/docs/extraction/nimclient.md) to the internal developer docs directory (nemo_retriever/developer_docs/nimclient.md), adds a redirect for legacy URLs, and updates import paths to match the current nemo_retriever.models.nim module layout.

• Content move & update: the guide is rewritten with corrected module paths (nemo_retriever.models.nim.util, nemo_retriever.models.nim.primitives, nemo_retriever.common.api.*), all of which resolve to existing packages in the repository.
• Navigation cleanup: the standalone "NimClient and custom NIM endpoints" nav entry is removed from section 8 of mkdocs.yml; a redirect to the new GitHub blob URL is added following the same pattern used for user-defined-stages.md.
• Cross-linking: a two-line pointer is added to nemo_retriever/src/nemo_retriever/graph/README.md and the new file is indexed in nemo_retriever/developer_docs/README.md.

Confidence Score: 5/5

Safe to merge — all changes are documentation reorganisation with no code or API surface affected.

The change is a documentation-only relocation. All updated import paths point to existing modules, the redirect follows an established pattern already present in mkdocs.yml, and the relative cross-link in the graph README resolves correctly. No code, configuration, or public API is modified.

nemo_retriever/developer_docs/nimclient.md — has a BOM character at line 1 and a minor env-var value inconsistency worth cleaning up before merging.

Important Files Changed

Filename	Overview
docs/mkdocs.yml	Removes nimclient nav entry from section 8 and adds a redirect from the old URL to the new GitHub blob location; follows the same external-URL redirect pattern already used for user-defined-stages.
nemo_retriever/developer_docs/README.md	Adds a single table row indexing the new nimclient.md alongside other internal guides; no issues.
nemo_retriever/developer_docs/nimclient.md	Content moved and updated with corrected module paths; has a UTF-8 BOM character at the start and a minor inconsistency between the env-var example value (NIM_MAX_RETRIES=5) and the documented function default (max_retries=10).
nemo_retriever/src/nemo_retriever/graph/README.md	Adds a two-line crosslink to the new NimClient developer doc; relative path resolves correctly.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["Legacy URL\n/extraction/nimclient/"] -->|mkdocs redirect| B["GitHub blob\nnemo_retriever/developer_docs/nimclient.md"]
    C["docs/mkdocs.yml nav\n(section 8)"] -- removed --> D["NimClient entry ❌"]
    E["nemo_retriever/developer_docs/README.md"] -->|indexed| B
    F["nemo_retriever/src/nemo_retriever/graph/README.md"] -->|crosslink| B
    B -->|relative link| F

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flowchart TD
    A["Legacy URL\n/extraction/nimclient/"] -->|mkdocs redirect| B["GitHub blob\nnemo_retriever/developer_docs/nimclient.md"]
    C["docs/mkdocs.yml nav\n(section 8)"] -- removed --> D["NimClient entry ❌"]
    E["nemo_retriever/developer_docs/README.md"] -->|indexed| B
    F["nemo_retriever/src/nemo_retriever/graph/README.md"] -->|crosslink| B
    B -->|relative link| F

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_{Reviews (3): Last reviewed commit: "docs(extraction): polish NimClient devel..." | Re-trigger Greptile}