docs: ADR-009 draft + versioning strategy — v3.1 PVE 9 only, v4.0 WebSocket
ADR-009 (draft) supersedes ADR-008 with confirmed PVE 9 support, the lun
integer fix approach, and a clear version→PVE support mapping:
- v3.0.x: PVE 8 + PVE 9, REST API
- v3.1.x: PVE 9 only, REST API, api() bump, snapshots
- v4.0.x: WebSocket JSON-RPC 2.0 — genuine architectural change, major version
ROADMAP: v3.2.0 renamed to v4.0.0 for WebSocket milestone; v3.1 scope updated
to document PVE 8 drop and reasons.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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