feat(skills): add comprehensive skill unit tests and fix mypy type narrowing [ticket-033]

[MatthiasLew]

Fixes mypy union-attr typecheck issue in validate.py and adds 9 unit tests in tests/test_skill.py covering all Data2DslSkill modes and adapters.

[ifuri-validator-agent]

Deterministic Validator approval for exact head 6b07ea8b6ff770442f3db9c5b112efd59f758ccf.

Ticket: ticket-033
Correlation ID: data2dsl-pr-33-ticket-033-6b07ea8b6f
Model: openrouter/z-ai/glm-5.2
Reviewed diff chunks: 2
Advisory LLM verdict: APPROVE
Advisory summary: Reviewed all 2 diff chunk(s). Chunk 1 of 2 introduces governance documentation for ticket-033, a mypy type narrowing fix in validate.py, a Code2Schema normalization fix in data2dsl_skill.py, and the beginning of a new test_skill.py suite. The visible code changes are low-risk, well-scoped, and aligned with the stated intent. The diff is truncated mid-file as expected for chunked review; semantic assessment is limited to visible content. | This chunk adds unit tests for Data2DslSkill.execute_compare covering curllm, code2logic, code2schema, missing inputs, and unknown adapter type scenarios. Tests assert expected statuses, outcomes, deltas, and error codes. No security concerns or test failures present.
Advisory findings: none
The LLM output above is advisory and was not used as the approval trust root.
Merge will be attempted after this approval when explicitly authorized.

Decision record (recomputable)

DECISION D-033-1119
TICKET ticket-033
HEAD_SHA 6b07ea8b6ff770442f3db9c5b112efd59f758ccf
CORRELATION_ID data2dsl-pr-33-ticket-033-6b07ea8b6f
ACTOR agent:ifuri-validator-agent[bot]
APPLIED_RULE P-CORE-015
INPUT author_login = "MatthiasLew"
INPUT observed_checks = ["governance / remote lifecycle=PASS"]
INPUT required_checks = ["governance / remote lifecycle"]
INPUT required_checks_source = "protected registry + GitHub applied rules (env/request)"
INPUT reviewer_login = "ifuri-validator-agent[bot]"
VERDICT APPROVE AUTHORITY DETERMINISTIC
REJECTED REQUEST_CHANGES BECAUSE NO_UNSAFE_CHANGE_REASON_FOUND
ADVISORY llm_verdict = "APPROVE" MODEL "openrouter/z-ai/glm-5.2"
ASSERT VERDICT_AUTHORITY != "ADVISORY"