Add initial local behavioral eval scaffold

[Shaelz]

• Adds a local/manual Codex behavioral-eval scaffold with a thin PowerShell entrypoint and dependency-free Node core.
• Adds an inspectable prompt corpus and external artifact output.
• Validates one fresh single-case vertical slice: explicit-dry-run-unfamiliar.
• Records deterministic artifact/file checks and proxy-only invocation evidence; does not claim direct skill-invocation observability or automatic pass/fail gating.
• Makes offline replay non-destructive by writing replay output separately from live evidence.
• Clarifies that current explicit tuned reusable framework-probe coverage is SvelteKit-specific; Laravel/PHP parity is deferred to a follow-up pass.
• States that no installer behavior, CI behavioral gate, plugin packaging, or live distribution behavior is changed.