ci: move builder image to the .NET 10 SDK

Jellyfin 12.0.0 targets net10.0, and the .NET 8 SDK refuses to even restore
a project that lists net10.0 among its TargetFrameworks (NETSDK1045) -- so
the multi-targeted net8.0;net10.0 build that will produce one plugin DLL per
Jellyfin generation cannot start until the builder image moves first.

Verified as a drop-in against the current net8-only master, inside the image:
restore + build are clean (0 errors, 0 warnings) and jprm produces the same
two-file zip as before. Analyzer levels still track each TFM, so the net8.0
leg stays warning-free; CA1873 will only need silencing on the net10.0 leg
once multi-targeting lands.

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

Dockerfile.builder

@@ -3,7 +3,7 @@
 # Build: docker build -f Dockerfile.builder -t gitea.tourolle.paris/dtourolle/srfplay-builder:latest .
 # Push:  docker push gitea.tourolle.paris/dtourolle/srfplay-builder:latest
 
-FROM mcr.microsoft.com/dotnet/sdk:8.0
+FROM mcr.microsoft.com/dotnet/sdk:10.0
 
 RUN apt-get update && apt-get install -y \
     python3 \

manifest-nightly.json

@@ -8,6 +8,14 @@
     "category": "Live TV",
     "imageUrl": "https://gitea.tourolle.paris/dtourolle/jellyfin-srfPlay/raw/branch/master/assests/main%20logo.png",
     "versions": [
+      {
+        "version": "1.0.20260903.198",
+        "changelog": "Nightly build 1.0.20260903.198 (699b543)",
+        "targetAbi": "10.9.0.0",
+        "sourceUrl": "https://gitea.tourolle.paris/dtourolle/jellyfin-srfPlay/releases/download/latest/srfplay_1.0.20260903.198.zip",
+        "checksum": "fcd415e82c95a6fe1e34db1d187a684f",
+        "timestamp": "2026-09-03T19:09:41Z"
+      },
       {
         "version": "1.0.20260627.189",
         "changelog": "Nightly build 1.0.20260627.189 (7c81ef9)",