feat(cccl): integrate missing CCCL directories — python/, ci/, .agent/, docs/, test/

Sparse-checkout from NVIDIA/cccl main branch to complete cccl_upstream:

Added:
- python/cuda_cccl/ (226 files) — Python bindings for device-level algorithms
  Critical for muh toolchain: cuda.compute.reduce_into, scan, radix_sort, etc.
  Includes 204 .py files with full test coverage for all 27 algorithms
- ci/ (163 files) — Build/test infrastructure
  build_cub.sh, test_cub.sh, build_and_test_targets.sh, matrix.yaml
  Directly maps to our [INFRA-CI] and [INFRA-BUILD] items
- .agent/skills/ (7 files) — NVIDIA's own agent skills for CCCL
  cccl-style/SKILL.md, cccl-test/SKILL.md, sass-diff/SKILL.md
- docs/ (491 files) — Official CCCL documentation
  CI references, CMake guides, Python compute docs, libcudacxx PTX docs
- test/ (12 files) — Top-level integration tests (cuda_smoke, stdpar)
- Root configs: .clang-format, .clang-tidy, CONTRIBUTING.md, pyproject.toml
- CLAUDE.md symlink → AGENTS.md (NVIDIA's standard)

cccl_upstream now mirrors full NVIDIA/cccl structure:
  Before: 42M (cub + thrust + libcudacxx + cudax + c + examples + benchmarks)
  After:  53M (+python +ci +docs +.agent +test +configs)

This completes the CCCL base needed for:
- [muh-bench] items: ci/util/build_and_test_targets.sh for targeted builds
- [CCCL-verify] items: python/cuda_cccl/tests/ as reference implementations
- [CCCL-test] items: ci/test_cub.sh, ci/test_thrust.sh
- Agent workflow: .agent/skills/ for consistent style and test patterns

cccl_upstream/docs/cccl/contributing/code_of_conduct.rst

@@ -0,0 +1,105 @@
+Code of Conduct
+===============
+
+Overview
+--------
+
+This document defines the Code of Conduct followed and enforced for
+NVIDIA C++ Core Compute Libraries.
+
+Intended Audience
+~~~~~~~~~~~~~~~~~
+
+-  Community
+-  Developers
+-  Project Leads
+
+Our Pledge
+----------
+
+In the interest of fostering an open and welcoming environment, we as
+contributors and maintainers pledge to making participation in our
+project and our community a harassment-free experience for everyone,
+regardless of age, body size, disability, ethnicity, sex
+characteristics, gender identity and expression, level of experience,
+education, socio-economic status, nationality, personal appearance,
+race, religion, or sexual identity and orientation.
+
+Our Standards
+-------------
+
+Examples of behavior that contributes to creating a positive environment
+include:
+
+-  Using welcoming and inclusive language.
+-  Being respectful of differing viewpoints and experiences.
+-  Gracefully accepting constructive criticism.
+-  Focusing on what is best for the community.
+-  Showing empathy towards other community members.
+
+Examples of unacceptable behavior by participants include:
+
+-  The use of sexualized language or imagery and unwelcome sexual
+   attention or advances.
+-  Trolling, insulting/derogatory comments, and personal or political
+   attacks.
+-  Public or private harassment.
+-  Publishing others' private information, such as a physical or
+   electronic address, without explicit permission.
+-  Other conduct which could reasonably be considered inappropriate.
+
+Our Responsibilities
+--------------------
+
+Project maintainers are responsible for clarifying the standards of
+acceptable behavior and are expected to take appropriate and fair
+corrective action in response to any instances of unacceptable behavior.
+
+Project maintainers have the right and responsibility to remove, edit,
+or reject comments, commits, code, wiki edits, issues, and other
+contributions that are not aligned to this Code of Conduct, or to ban
+temporarily or permanently any contributor for other behaviors that they
+deem inappropriate, threatening, offensive, or harmful.
+
+Scope
+-----
+
+This Code of Conduct applies both within project spaces and in public
+spaces when an individual is representing the project or its community.
+Examples of representing a project or community include using an
+official project email address, posting via an official social media
+account, or acting as an appointed representative at an online or
+offline event. Representation of a project may be further defined and
+clarified by project maintainers.
+
+Enforcement
+-----------
+
+Instances of abusive, harassing, or otherwise unacceptable behavior may
+be reported by contacting cpp-conduct@nvidia.com. All complaints will be
+reviewed and investigated and will result in a response that is deemed
+necessary and appropriate to the circumstances. The project team is
+obligated to maintain confidentiality with regard to the reporter of an
+incident. Further details of specific enforcement policies may be posted
+separately.
+
+Project maintainers who do not follow or enforce the Code of Conduct in
+good faith may face temporary or permanent repercussions as determined
+by other members of the project's leadership.
+
+Attribution
+-----------
+
+This Code of Conduct was taken from the `NVIDIA
+RAPIDS <https://docs.rapids.ai/resources/conduct/>`_ project, which was
+adapted from the `Contributor Covenant version
+1.4 <https://www.contributor-covenant.org/version/1/4/code-of-conduct.html>`_.
+
+Please see this `FAQ <https://www.contributor-covenant.org/faq>`_ for
+answers to common questions about this Code of Conduct.
+
+Contact
+-------
+
+Please email cpp-conduct@nvidia.com for any Code of Conduct related
+matters.