AGENTS.md: slow first start with GStreamer and Smart App Control

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

AGENTS.md

@@ -46,6 +46,9 @@ hook-based, so upstream can still be merged.
   `Themes/Vocaluxe 2024/*.mp4` videos) from the upstream Nightly zip
   (github.com/Vocaluxe/Vocaluxe/releases/tag/Nightly, `Vocaluxe_Nightly_Windows_x64.zip`); the PitchTracker source is
   unchanged in this fork. Both are gitignored. Data and `Config.xml` are in `Output` (non-installer builds).
+- First start is slow on Windows with Smart App Control: GStreamer (default `PlayBackLib`) scans its 216 plugins once
+  and each unsigned DLL is checked (~19 min on DisiFramework, window "not responding" in "Init Playback"). Later starts
+  are fast. `<Sound><PlayBackLib>PortAudio</PlayBackLib></Sound>` in `Config.xml` avoids GStreamer.
 - Building rewrites the copyright year in `Vocaluxe/Properties/AssemblyInfo.cs`; don't commit that.
 - Don't use `dotnet sln add`: it rewrites the configuration table of `Vocaluxe.sln`. Copy the lines of `VocaluxeWeb`.
 - New `config.xml` fields must also go into `Tests/VocaluxeLib/XML/TestFiles/SConfig.xml` (round-trip test; CRLF).