AL2023 release-version drift tracking

[pachev]

Context

AL2023 has two update concepts:

1. Per-package updates via dnf check-update (handled in v0.3 — same model as apt).
2. Release-version bumps via dnf check-release-update — AWS pins the distro to dated releases (e.g. 2023.9.20251208) and the whole userland upgrades atomically with dnf upgrade --releasever=<version>.

(2) doesn't fit the per-package updates_available model, so we punted on it.

Proposal

Track release drift as a separate signal on the server row:

• release_version (current, parsed from /etc/os-release VERSION_ID or similar)
• latest_release_version (newest version reported by dnf check-release-update)
• release_update_available (boolean)
• last_release_check (timestamp)

Surface on the server detail view as a distinct row, not bundled with the package-update count. Apply path is its own thing (dnf upgrade --releasever=...), separate from the per-package apply flow.

Scope

• AL2023 (amzn) only for now. Other dnf distros (Fedora/Rocky/RHEL) don't have the same dated-release model.
• Read-only first: detect drift, surface in UI. Apply flow is a follow-up.

Out of scope

• Per-package patching (covered by v0.3 dnf support).
• Major-version jumps (AL2023 → AL2024, when that exists).