Alpha gate E tail: C#-native bad/ok example pairs mirroring the .own gallery

[PhysShell]

Agent brief — tier: basic. One PR (Closes #<this>); branch from main. House rules: AGENTS.md.

Goal

Gate E of docs/notes/alpha-readiness.md is built for .own (12 test-pinned gallery cases) but the C# audience needs .cs-native bad/ok pairs.

Sources of truth

• examples/gallery/*.own — the 12 pinned cases (incl. 00_ok_clean).
• Existing extractor samples (e.g. DiCaptiveSample.cs, StaticEventEscapeViewModel) — match their layout and style.
• .github/workflows/ci.yml — how extractor samples are wired into CI (e.g. the wpf-extractor job).

Deliverable

• For each gallery case expressible in real C#: a bad/ok C# pair under examples/, following the existing sample conventions.
• CI wiring so the extractor + core pipeline runs them: the bad variant must produce the expected diagnostic code, the ok variant must be clean.
• Cases not expressible in C# (pure .own semantics) are skipped with a written reason in the PR description — do not force them.

Guardrails

• There is no local dotnet in agent environments: the C# frontend is CI-validated only. Success is a green CI run with the expected diagnostics, not "it should compile".
• Do not change extractor behaviour to make an example pass; if an example exposes a real extractor gap, record it in the PR description instead.

Done when

Pairs are committed, CI job(s) green, expected diagnostic codes pinned per bad example; python tests/run_tests.py and ruff check . clean.