readme: runnable quickstarts, v0.1.0 status, measured perf ranges

[eitamring]

Docs-only, pre-launch hardening from the fresh-clone repro gate.

• Every README example block now runs literally from a fresh clone: make build once, then ./bin/classmesh (the bare classmesh form assumed a binary on PATH).
• Status line reworded to "v0.1.0, working toward v1"; the repo had no tags while claiming v1. v0.1.0 gets tagged on main after this merges.
• Perf table rows aligned with what make bench reproduces today (count=3 on the README's reference machine): full pipeline 500-550 ns (~1.8M records/sec), rules worst case 7-8 us (~130k records/sec). First-rule 46 ns row unchanged (measured 45.9-49.6).

Verified: fresh clone runs both 1M-line demos with exact documented stats (processed=1000000 classified=940162 review=59838; 1.51s wall).