Port to Jellyfin 12.0 (net10.0, targetAbi 12.0.0.0)

- csproj: net9.0 -> net10.0, version 2.1.0.0 -> 3.0.0.0
- Jellyfin.Controller 10.*-* -> 12.*-* with ExcludeAssets="runtime"
- drop redundant Microsoft.Extensions.Http ref (NU1510 under the .NET 10 SDK;
  IHttpClientFactory comes from the Microsoft.AspNetCore.App framework ref)
- NetAnalyzers 9.0.0 -> 10.0.100
- Endpoints: bare [Authorize] -> [Authorize(Policy = "DefaultAuthorization")]
  now that legacy authorization is disabled by default
- drop unused using in AnilistApi.cs
- build.yaml + manifest.json: 3.0.0.0 / abi 12.0.0.0 entry
- gitignore local dist/ release-artifact dir

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitignore

@@ -328,3 +328,6 @@ ASALocalRun/
 
 # MFractors (Xamarin productivity tool) working folder 
 .mfractor/
+
+# Local release artifacts
+dist/