fix: netavark GLIBC mismatch in ISO, container adopt, app updates

ISO build no longer copies netavark from build host (Debian 13/GLIBC 2.41)
which broke container networking on Debian 12 targets. Rootfs already
installs netavark from Debian 12 repos — just configure the backend.

Install RPC now adopts existing containers (from first-boot) instead of
erroring on duplicates. Container scanner extracts real versions from
image tags and detects available updates against pinned versions.

Frontend shows update button with version info when updates are available.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

core/archipelago/src/data_model.rs

@@ -116,6 +116,7 @@ pub enum PackageState {
     Removing,
     #[serde(rename = "backing-up")]
     BackingUp,
+    Updating,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
@@ -133,6 +134,9 @@ pub struct PackageDataEntry {
     pub installed: Option<InstalledPackageDataEntry>,
     #[serde(rename = "install-progress")]
     pub install_progress: Option<InstallProgress>,
+    /// Pinned image version from image-versions.sh when it differs from running version
+    #[serde(rename = "available-update", skip_serializing_if = "Option::is_none")]
+    pub available_update: Option<String>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]