docs: make the README an entry point, not a manual master
The README had grown into a 410-line flag reference whose status section was false -- it claimed no artifact was admitted and described as blocked several rows the gate has since closed. A reader could not tell what Stream is, and an operator could not trust what it said. Reference material moves to docs/{configuration,cli,testing}.md; the README keeps what it is, what is actually proved (23 verified, 4 partial, none blocked), and a map of where to look. The configuration audit had drifted the same way: eleven rows still cited blockers the gate records as closed -- cold-replay holes, planBackfill false-negatives, retry-supervisor health, the reconnect race, persisted host parking. Five of those rows had no remaining limitation at all, so they were promoted rather than left understating what holds. The deployment gate itself is unchanged. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>