Refresh README benchmarks

[tolgaergin]

Summary

• rewrite the root README around the current CLI/product positioning
• add tracked VitePress docs benchmark fixture and README benchmark artifacts
• add up-to-date mode support to the install readiness harness
• update README benchmark tables with install, firewall monitor, run/bin, TSX, lint, and fmt results

Validation

• cargo build --release --locked -p lpm-cli --bin lpm-rs
• node bench/scripts/run-install-readiness.mjs --self-test
• node bench/scripts/run-bin-benchmark.mjs --self-test
• node bench/scripts/run-install-readiness.mjs --samples 10 --fixtures vitepress --managers lpm,bun,pnpm,npm --modes cold,warm,up-to-date --lpm-firewall-modes off,report --lpm-bin target/release/lpm-rs
• ITERATIONS=10 WARMUP_ITERATIONS=2 SCENARIOS=... GROUPS=... RUNNERS=... node bench/scripts/run-bin-benchmark.mjs
• ITERATIONS=10 WARMUP_ITERATIONS=2 MODULE_COUNTS=10 SCENARIOS=... node bench/scripts/exec-runtime-benchmark.mjs
• RUNS=10 LPM_BIN=target/release/lpm-rs ./bench/run.sh builtin-tools
• git diff --check