Add Hamilton dataflow example with declarative driver and tests

[2-Coatl]

Summary

• add the ExecPlan describing the TDD workflow for the Hamilton Data→Prompt→LLM pipeline example
• implement a minimal Hamilton-style driver, declarative dataflow functions, and a deterministic mock LLM client under scripts/coding/ai/examples/hamilton_llm/
• introduce dedicated pytest coverage for the example and document the new asset in the Hamilton governance guide and docs index

Testing

• python3 -m pytest scripts/coding/tests/ai/examples/test_hamilton_llm_example.py
• python3 -m pytest docs/qa/testing/test_documentation_alignment.py (fails due to pre-existing documentation debt; unchanged by this PR)

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Codex Task