remove custom-metadata.md; canonical path is vdbs + notebooks

[kheiss-uwzoo]

Summary

• Remove docs/docs/extraction/custom-metadata.md (duplicate of notebook + VDB README content added in align metadata docs with VDB filtering guide #2108).
• Expand Metadata and filtering on �dbs.md with a short overview and links to the worked notebooks.
• Drop the separate MkDocs nav entry; add redirect custom-metadata.md -> �dbs.md#metadata-and-filtering.
• Update cross-links and doc-snippet test registry.

Follows Julio's NVBugs 6205401 guidance: VDB/metadata facts live on �dbs.md; runnable walkthroughs stay in notebooks.

Notebooks (canonical examples)

• metadata_and_filtered_search.ipynb
• nemo_retriever_retriever_query_metadata_filter.ipynb

Operator/API reference remains in nemo_retriever/src/nemo_retriever/vdb/README.md.

Test plan

• MkDocs build; confirm redirect from old custom-metadata URL
• Nav no longer lists a separate Custom metadata page
• Notebook links resolve on GitHub

[greptile-apps]

Greptile Summary

This PR removes two redundant documentation files (custom-metadata.md and integrations-langchain-llamaindex-haystack.md), consolidates metadata content into the existing vdbs.md page, and adds MkDocs redirects so existing bookmarks and links continue to resolve.

• Consolidated metadata docs: The #metadata-and-filtering section in vdbs.md is expanded with the sidecar parameter overview, retriever service flow, and links to both canonical notebooks, replacing the standalone page.
• Updated cross-links: All in-page references to the two deleted files are rewritten to point at the relevant sections on vdbs.md or notebooks/index.md across five files.
• Test registry updated: _PUBLIC_RETRIEVER_DOCS in the documentation snippet test swaps the deleted custom-metadata.md for vdbs.md, so Python blocks in the surviving page remain validated for unsupported constructor kwargs.

Confidence Score: 5/5

Safe to merge — purely a documentation restructure with no code logic changes.

All changes are documentation and test-registry updates. Both previously flagged issues (bare metadata section and missing notebook link) are resolved in this revision. The MkDocs redirects correctly point deleted URLs at the right destinations, the expanded metadata section in vdbs.md accurately describes the sidecar parameters and service flow, and the Python snippet test continues to cover vdbs.md. No source code is modified.

No files require special attention; the one minor gap is that metadata_and_filtered_search.ipynb is not added to the documentation snippet test registry alongside the other metadata notebook.

Important Files Changed

Filename	Overview
docs/docs/extraction/vdbs.md	Metadata and filtering section expanded with sidecar parameter prose, retriever service flow, and notebook links — addresses previously flagged bare-link issue.
docs/docs/extraction/notebooks/index.md	Both canonical metadata notebooks now listed: metadata_and_filtered_search.ipynb and nemo_retriever_retriever_query_metadata_filter.ipynb — addresses previously flagged missing link.
docs/mkdocs.yml	Nav sections renumbered after removing two entries; redirects added for both deleted pages including fragment anchor target for custom-metadata.md.
nemo_retriever/tests/test_src_documentation_snippets.py	_PUBLIC_RETRIEVER_DOCS updated to reference vdbs.md instead of the deleted custom-metadata.md; existing Python block in vdbs.md is valid and uses no unsupported Retriever kwargs.
docs/docs/extraction/custom-metadata.md	Deleted; content migrated to vdbs.md#metadata-and-filtering and canonical runnable examples remain in the two linked notebooks.
docs/docs/extraction/integrations-langchain-llamaindex-haystack.md	Deleted; LangChain and LlamaIndex notebook links survive in notebooks/index.md; MkDocs redirect added to notebooks/index.md.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["custom-metadata.md\n(deleted)"] -->|"301 redirect"| B["vdbs.md#metadata-and-filtering"]
    C["integrations-langchain-llamaindex-haystack.md\n(deleted)"] -->|"301 redirect"| D["notebooks/index.md"]

    B --> E["sidecar params overview\nmeta_dataframe / meta_source_field / meta_fields"]
    B --> F["nemo_retriever_retriever_query_metadata_filter.ipynb\n(worked example)"]
    B --> G["VDB README\n(operator reference)"]

    D --> H["metadata_and_filtered_search.ipynb"]
    D --> F
    D --> I["LangChain / LlamaIndex notebooks"]

    J["workflow-agentic-retrieval.md\nagentic-retrieval-concept.md\ndeployment-options.md\noverview.md\nworkflow-e2e-blueprints.md"] -->|"cross-links updated"| B
    J -->|"cross-links updated"| D

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flowchart TD
    A["custom-metadata.md\n(deleted)"] -->|"301 redirect"| B["vdbs.md#metadata-and-filtering"]
    C["integrations-langchain-llamaindex-haystack.md\n(deleted)"] -->|"301 redirect"| D["notebooks/index.md"]

    B --> E["sidecar params overview\nmeta_dataframe / meta_source_field / meta_fields"]
    B --> F["nemo_retriever_retriever_query_metadata_filter.ipynb\n(worked example)"]
    B --> G["VDB README\n(operator reference)"]

    D --> H["metadata_and_filtered_search.ipynb"]
    D --> F
    D --> I["LangChain / LlamaIndex notebooks"]

    J["workflow-agentic-retrieval.md\nagentic-retrieval-concept.md\ndeployment-options.md\noverview.md\nworkflow-e2e-blueprints.md"] -->|"cross-links updated"| B
    J -->|"cross-links updated"| D

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_{Reviews (18): Last reviewed commit: "Merge branch 'main' into docs/consolidat..." | Re-trigger Greptile}