snip v0.1.1 — framework v2

snip v0.1.1 — framework v2

Adds the §15–§18 artifacts:

• docs/threat-model.md — adversary: attacker crafting LLM-generated diffs that bypass static rules via novel encodings.
• tools/dev/repro.sh — (host, rustc-version)-keyed baseline; no toolchain pin.
• SECURITY.md — GHSA tab, 14/90-day window.
• tools/perf/budget.md — snip check on 200 KiB diff: 400 ms median ±25%.
• tests/integration.rs + tools/perf/bench.rs — #[test] with std::time median-of-5.
• CHANGES.md — 0.1.1 block with the v2 additions.

Pre-1.0.0: GHSA-only security advisories; CVEs reserved for 1.0.0+.

Bench and repro.sh will activate once Cargo.toml and src/ land.