refactor(nodes)!: rename typed constructor config to data

[WH-2099]

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Related Issue

Closes #47

Summary

This follow-up to #38 / #39 renames the typed node-constructor keyword from config to data now that direct instantiation accepts concrete *NodeData payloads instead of raw {id, data} config objects.

What changed:

• renamed Node.__init__(..., config=...) to Node.__init__(..., data=...)
• updated concrete node subclasses to forward data= instead of config=
• updated direct instantiation call sites in examples and tests
• left raw graph boundary types such as NodeConfigDict unchanged

Why it changed:

• config still refers to the outer graph payload in this codebase
• the constructor now receives the inner typed node data payload
• nodes that already depend on real *_config collaborators read more clearly after the rename

Developer impact:

• direct keyword construction now uses data= instead of config=
• raw graph parsing code that still works with NodeConfigDict is unchanged

Validation:

• make check
• uv run pytest tests/graph/test_graph_validation.py tests/http/test_client.py tests/nodes/parameter_extractor/test_prompts.py tests/nodes/variable_assigner/test_v1_node.py tests/nodes/variable_assigner/test_v2_node.py

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Checklist

• This pull request links the issue it resolves or advances
• This pull request title follows Conventional Commits, and any breaking change is marked with !
• If CLA Assistant prompted me, I signed CLA.md in the pull request conversation