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/cudax/graph.rst

@@ -0,0 +1,52 @@
+.. _cudax-graph:
+
+Graphs library
+==============
+
+.. toctree::
+   :glob:
+   :maxdepth: 1
+
+   api/struct*graph*
+
+The headers of the graph library provide facilities to create and manage CUDA graphs.
+
+This library is under construction and not yet ready for production use.
+
+.. list-table::
+   :widths: 25 45 30
+   :header-rows: 0
+
+   * - :ref:`<cuda/experimental/graph.cuh> <cudax-graph-graph-builder>`
+     - Class `cuda::experimental::graph_builder`: An owning wrapper for a `cudaGraph_t` object.
+     - cudax 2.9.0 / CCCL 2.9.0
+   * - :ref:`<cuda/experimental/graph.cuh> <cudax-graph-graph-node-ref>`
+     - Class `cuda::experimental::graph_node_ref`: A non-owning wrapper for a `cudaGraphNode_t` object.
+     - cudax 2.9.0 / CCCL 2.9.0
+   * - :ref:`<cuda/experimental/graph.cuh> <cudax-graph-graph>`
+     - Class `cuda::experimental::graph`: An owning wrapper for a `cudaGraphExec_t` object.
+     - cudax 2.9.0 / CCCL 2.9.0
+
+.. _cudax-graph-graph-builder:
+
+graph_builder
+-------------
+
+``cuda::experimental::graph_builder`` is an owning wrapper for a ``cudaGraph_t`` object.
+See the API reference entries in this section for details.
+
+.. _cudax-graph-graph-node-ref:
+
+graph_node_ref
+--------------
+
+``cuda::experimental::graph_node_ref`` is a non-owning wrapper for a ``cudaGraphNode_t`` object.
+See the API reference entries in this section for details.
+
+.. _cudax-graph-graph:
+
+graph
+-----
+
+``cuda::experimental::graph`` is an owning wrapper for a ``cudaGraphExec_t`` object.
+See the API reference entries in this section for details.