docs/configuration.md still says `worker.backend: local` is "not live yet" — it shipped

\`docs/configuration.md\` (around lines 112–114 and 382–385) carries \`# NOT LIVE YET\` markers and the sentence *"setting \`worker.backend: local\` today fails at task start with \`unknown coding backend 'local'\`"*, and its \`worker.backend\` table row offers only \`claude\` or \`codex\`. It is live: \`\`\` $ python -c "from no_human.agent.backend import SUPPORTED_BACKENDS; print(SUPPORTED_BACKENDS)" ('claude', 'codex', 'local') $ nh task add --help | grep -A1 backend --backend [claude|codex|local] Run THIS task's coder on the named backend \`\`\` and \`docs/BACKENDS.md\` documents \`local\` end to end. The two docs contradict each other. **Fix:** remove the three "not live yet" markers and the stale error sentence, add \`local\` to the \`worker.backend\` row with a pointer to \`BACKENDS.md\`. Docs only, under 20 lines.