XY-913: Reuse operator snapshots for status

[yvette-carlisle]

Summary

• let non-live decodex status reuse the local operator listener snapshot when it is fresh and covers the requested project
• add status source/age readback plus scoped project ids for cached projection
• fall back safely to local runtime status with status_cached_snapshot_unavailable details when cache reuse is unsafe
• update README and operator control-plane docs for the new status path

Validation

• cargo test -p decodex status_cache --all-features -- --test-threads=1
• cargo test -p decodex status_snapshot --all-features -- --test-threads=1
• cargo clippy --all-features --all-targets -p decodex -- -D warnings
• cargo make test
• python3 /Users/x/.codex/plugins/cache/hack-ink/playbook/0.3.0/scripts/semantic_drift_audit.py --rev HEAD with agent verdict: pass
• cargo make check
• runtime smoke against old installed listener fell back safely with status_cached_snapshot_unavailable instead of trusting an incompatible cached snapshot