M6 epic: VM/LXC associations and guest agent data

[Andreas-Froyland]

Tracking issue. Dependency and status checklists only — implementation stays in narrow linked issues.

Outcome

QEMU and LXC guests are discovered, normalized, and associated with Fleet machines, including guest-agent data with explicit unavailable states.

Supersedes

Replaces the guest inventory and machine-association parts of #3's manifest wiring.

Depends on

• M6 Proxmox accounts and discovery
• M2 machine, endpoint, and observation model

Scope checklist

• QEMU/LXC discovery with per-resource failure isolation
• Stable association between a Proxmox guest and a Fleet machine identity
• QEMU Guest Agent readiness and IP data, tolerant of loose or null API shapes
• Explicit unavailable states rather than silently empty fields

Constrained by

• docs/PLAN.md — M6; ADR-0005: provider DTOs translate at the boundary
• Version-specific API differences stay behind the provider

Non-goals

• Lifecycle actions (separate epics)
• Correlating guests into Fleet machines without displayed evidence