release: 0.2.1

[Obsecurus]

Summary

• prepare 0.2.1 release with fbhash backend, sigma condition flow, and vectorscan regex-engine scaffold
• add public scenario corpora (PCAP replay, firmware blobs, sigma/log/dns) with provenance and replay tooling
• add stats contract tests, STATS.md docs, and website updates including demo reels + stats visualization

Validation

• cargo fmt --all --check
• cargo test --workspace
• cargo build --release
• ci/generate_cli_assets.sh /tmp/precursor-cli-assets ./target/release/precursor
• ci/benchmark_scenarios.sh ./target/release/precursor benchmarks/latest.md
• PRECURSOR_MRSHV2_LIB_DIR= cargo test --workspace --features similarity-mrshv2

Release notes

• Cargo version bumped to 0.2.1
• CHANGELOG.md updated for 0.2.1