D9: Multi-instance semantics and reported version string

[thedancingdeveloper]

Arr users commonly run two instances (1080p / 4K). Does one StackArr present as two Sonarrs, or does the unified model make that obsolete?

Also: clients gate features on /api/v3/system/status version. Pick it deliberately.

Acceptance: instance-identity design and version string recorded before T39-T41.

[thedancingdeveloper]

🤖 Vogt validation pass — 2026-08-20 (automated review vs dd26a0aa)

Needs maintainer decision — a product/design call the code cannot answer. This is D9, tracking §10 open questions #6 (reported version string) and #7 (multi-instance semantics), both still listed as unresolved in docs/UNIFIED-ARR-PLAN.md. No arr façade exists yet at HEAD (no stackarr-compat-* crates; /api/v3/system/status is not served with a deliberately chosen version), so neither the instance-identity model nor the version string has been decided in code. The plan requires this recorded before T39-T41, which are not started. Open and pending a decision.