Add Jellyfin 12.0 release build alongside 10.11

Multi-target the plugin against net9.0 (Jellyfin 10.11.x) and net10.0
(Jellyfin 12.0.x), with per-framework Jellyfin.Controller/Model references.

Jellyfin 12 added a controlling-session parameter to
ISessionManager.ReportCapabilities; an empty value skips the AssertCanControl
check, which is what a server-side registration needs.

Each release now ships two packages, jellylms_<version>_jf11.zip and
jellylms_<version>_jf12.zip, with a manifest entry each. Jellyfin filters by
targetAbi, so both can share a version number. Also corrects the manifest
targetAbi for new releases from 10.10.0.0 to 10.11.0.0 - the plugin has
referenced 10.11 packages since 1.0.0.

jprm only reads ./build.yaml, so build-plugin.sh swaps targetAbi/framework per
variant and restores the file afterwards.

The builder image moves to the .NET 10 SDK, which targets both frameworks.
CA1873 (new in that SDK) is disabled alongside CA1848, same rationale.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

jellyfin.ruleset

@@ -100,6 +100,8 @@
         <Rule Id="CA1308" Action="None" />
         <!-- disable warning CA1848: Use the LoggerMessage delegates -->
         <Rule Id="CA1848" Action="None" />
+        <!-- disable warning CA1873: Evaluation of logging argument may be expensive (same rationale as CA1848) -->
+        <Rule Id="CA1873" Action="None" />
         <!-- disable warning CA2101: Specify marshaling for P/Invoke string arguments -->
         <Rule Id="CA2101" Action="None" />
         <!-- disable warning CA2234: Pass System.Uri objects instead of strings -->