Polish public docs packaging: operator runbook, README completeness

[Velascat]

Context

The repo is now public. The README and docs/ directory cover setup and runtime, but there are gaps in operator-facing content: the tuning loop is undocumented, the PR review guide doesn't exist, and the demo isn't positioned as a validation ritual.

Goal

Complete the operator documentation suite so a new operator can run the full stack with confidence:

1. docs/operator/tuning.md — threshold tuning loop
2. docs/operator/pr_review.md — PR review loop guide
3. docs/operator/runtime.md — reinforce dry-run-first posture for autonomy-cycle
4. README — link all operator docs, position demo as ritual
5. docs/backlog.md — reflect post-hardening priorities

Acceptance Criteria

• All four operator docs exist and are cross-linked
• README operator section is complete
• docs/backlog.md is up to date

Labels

documentation, operator-docs