fix(db): restore the PostgreSQL upgrade path

The v12.0 rebase replaced the PostgreSQL provider's initial migration instead of
adding to it, so an existing database kept the pre-12.0 schema while the code
migrations ran against it and startup aborted on a missing NormalizedUsername.

- restore 20260305010333_InitialPostgreSql as the baseline
- add 20260306000000_UpgradeToServer12Schema carrying it to the 12.0 model
- convert OwnerId and PrimaryVersionId to uuid with explicit casts, clear
  unparseable ids and repoint dangling owners at the placeholder item
- drop orphaned permissions and preferences before UserId becomes non-nullable
- add 20260524120336_AddUniqueNormalizedUsernameIndex after the code migration
  that fills the column in
- read an empty or unknown encoding.xml EncoderPreset as the default
- cover both paths against a real PostgreSQL and guard the migration ordering

tests/Jellyfin.Model.Tests/Configuration/EncodingOptionsTests.cs

@@ -0,0 +1,50 @@
+using System.IO;
+using System.Xml.Serialization;
+using MediaBrowser.Model.Configuration;
+using MediaBrowser.Model.Entities;
+using Xunit;
+
+namespace Jellyfin.Model.Tests.Configuration;
+
+public class EncodingOptionsTests
+{
+    [Theory]
+    [InlineData("<EncoderPreset></EncoderPreset>")]
+    [InlineData("<EncoderPreset />")]
+    [InlineData("<EncoderPreset>  </EncoderPreset>")]
+    [InlineData("<EncoderPreset>notapreset</EncoderPreset>")]
+    public void Deserialize_UnreadableEncoderPreset_FallsBackToDefault(string encoderPresetElement)
+    {
+        var options = Deserialize($"<EncodingOptions>{encoderPresetElement}<H264Crf>21</H264Crf></EncodingOptions>");
+
+        Assert.Equal(EncoderPreset.auto, options.EncoderPreset);
+
+        // The rest of the file has to survive: a throwing preset used to discard every other encoding setting.
+        Assert.Equal(21, options.H264Crf);
+    }
+
+    [Fact]
+    public void Deserialize_KnownEncoderPreset_IsKept()
+    {
+        var options = Deserialize("<EncodingOptions><EncoderPreset>veryfast</EncoderPreset></EncodingOptions>");
+
+        Assert.Equal(EncoderPreset.veryfast, options.EncoderPreset);
+    }
+
+    [Fact]
+    public void Serialize_WritesTheEncoderPresetElement()
+    {
+        var serializer = new XmlSerializer(typeof(EncodingOptions));
+        using var writer = new StringWriter();
+        serializer.Serialize(writer, new EncodingOptions { EncoderPreset = EncoderPreset.slow });
+
+        Assert.Contains("<EncoderPreset>slow</EncoderPreset>", writer.ToString(), System.StringComparison.Ordinal);
+    }
+
+    private static EncodingOptions Deserialize(string xml)
+    {
+        var serializer = new XmlSerializer(typeof(EncodingOptions));
+        using var reader = new StringReader(xml);
+        return (EncodingOptions)serializer.Deserialize(reader)!;
+    }
+}