Update RMM docs to use NVIDIA theme

[bdice]

Description

Updates the RMM docs to use the NVIDIA Sphinx theme, removes the local RAPIDS custom CSS/JS includes that are injected by docs post-processing, disables Doxygen dot graph generation to avoid the Graphviz/GTK/Wayland dependency chain, and adds context to the C++ memory resources landing page.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

Validation: ran make clean; make html from docs/; commit hooks passed.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR migrates the documentation infrastructure from PyData Sphinx theme to NVIDIA Sphinx theme, removes Graphviz-based diagram generation across both Python and C++ documentation pipelines, updates the copyright year to 2026, and standardizes the project name capitalization.

Changes

Documentation Theme and Infrastructure Migration

Layer / File(s)	Summary
Sphinx Configuration Migration docs/conf.py	Sphinx configuration switches from pydata_sphinx_theme to nvidia_sphinx_theme, the copyright year extends to 2026, the project name changes to capitalized RMM, and external custom CSS/JS asset registration is removed.
Python Environment and Dependency Updates dependencies.yaml, conda/environments/all_cuda-129_arch-aarch64.yaml, conda/environments/all_cuda-129_arch-x86_64.yaml, conda/environments/all_cuda-132_arch-aarch64.yaml, conda/environments/all_cuda-132_arch-x86_64.yaml	All dependency declarations consistently remove graphviz and pydata-sphinx-theme>=0.15.4, and add nvidia-sphinx-theme as a pip-installed package across four conda environment variants and the root dependency manifest.
C++ Documentation Infrastructure Adjustments cpp/doxygen/Doxyfile, cpp/doxygen/header.html	Doxygen configuration disables HAVE_DOT to turn off Graphviz diagram generation, and the Doxygen header template removes external RAPIDS custom JavaScript and CSS includes.
Memory Resources Documentation docs/cpp/memory_resources/index.md	Introductory content added describing RMM memory resources, their role in governing allocation/deallocation for different memory types, and how adaptors wrap upstream resources to modify behavior.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Suggested labels

non-breaking, improvement

Suggested reviewers

• msarahan
• KyleFromNVIDIA

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title 'Update RMM docs to use NVIDIA theme' accurately reflects the main change: switching the documentation theme from pydata-sphinx-theme to nvidia-sphinx-theme.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The pull request description accurately describes the changeset, including theme migration, dependency removal, Doxygen configuration changes, and documentation improvements.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

🧹 Nitpick comments (1)

dependencies.yaml (1)

349-350: ⚡ Quick win

Consider pinning nvidia-sphinx-theme version.

Installing nvidia-sphinx-theme without a version constraint could lead to unexpected breaking changes if the theme is updated. Consider adding a version range for stability.

📌 Suggested version constraint

           - pip:
-              - nvidia-sphinx-theme
+              - nvidia-sphinx-theme>=1.0,<2.0

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@dependencies.yaml` around lines 349 - 350, The pip dependency entry for
nvidia-sphinx-theme is unpinned; update the dependencies.yaml pip list entry for
nvidia-sphinx-theme to include an explicit version constraint (either a fixed
version like ==X.Y.Z or a safe range like >=X.Y,<X+1.0 or ~=X.Y) to prevent
accidental breaking changes; locate the nvidia-sphinx-theme item in the pip list
and replace the bare name with the chosen versioned specifier and run dependency
resolution to verify compatibility.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@dependencies.yaml`:
- Around line 349-350: The pip dependency entry for nvidia-sphinx-theme is
unpinned; update the dependencies.yaml pip list entry for nvidia-sphinx-theme to
include an explicit version constraint (either a fixed version like ==X.Y.Z or a
safe range like >=X.Y,<X+1.0 or ~=X.Y) to prevent accidental breaking changes;
locate the nvidia-sphinx-theme item in the pip list and replace the bare name
with the chosen versioned specifier and run dependency resolution to verify
compatibility.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 5e3a806b-1bb6-4190-8c0a-d864b8d0ad5e

📥 Commits

Reviewing files that changed from the base of the PR and between a66679d and 45856ef.

📒 Files selected for processing (9)

• conda/environments/all_cuda-129_arch-aarch64.yaml
• conda/environments/all_cuda-129_arch-x86_64.yaml
• conda/environments/all_cuda-132_arch-aarch64.yaml
• conda/environments/all_cuda-132_arch-x86_64.yaml
• cpp/doxygen/Doxyfile
• cpp/doxygen/header.html
• dependencies.yaml
• docs/conf.py
• docs/cpp/memory_resources/index.md

💤 Files with no reviewable changes (1)

• cpp/doxygen/header.html

[josephine-wolf-oberholtzer]

Sphinx changes LGTM. Can't comment on the rest.

[wence-]

nit: I would probably remove this sentence.