v0.6.8

Added

• Automated performance benchmarks in CI: A new benchmark workflow runs on every push to main. It executes cargo bench for both search_benchmark and persistence_benchmark suites using the Criterion bencher output format, runs the validator binary in JSON mode for functional performance validation, and uploads results as a benchmark-results artifact. Historical trends are tracked in the gh-pages branch via benchmark-action/github-action-benchmark, with automatic alerts on >200% regressions.
• Registered persistence_benchmark in Cargo.toml: The benches/persistence_benchmark.rs suite (save/load index, trigram deserialization, file staleness checks) was already present but not declared as a [[bench]] target. It is now runnable via cargo bench --bench persistence_benchmark.