recognize underscore and dot separators for multi-version grouping (#16465)

* Add underscore and dot as multi-version file separators

Extend IsEligibleForMultiVersion to recognize _ and . as valid
separators between the base movie name and the version suffix.

Common naming patterns like 'Movie_4K.mkv' or 'Movie.UHD.mkv'
are now correctly grouped as alternate versions during library scan.

* Address review: remove comment, add 3D recognition assertions

---------

Co-authored-by: aimarshall615-creator <aimarshall615@gmail.com>

Emby.Naming/Video/VideoListResolver.cs

@@ -217,6 +217,8 @@ namespace Emby.Naming.Video
             // The CleanStringParser should have removed common keywords etc.
             return testFilename.IsEmpty
                    || testFilename[0] == '-'
+                   || testFilename[0] == '_'
+                   || testFilename[0] == '.'
                    || CheckMultiVersionRegex().IsMatch(testFilename);
         }
     }

tests/Jellyfin.Naming.Tests/Video/MultiVersionTests.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using Emby.Naming.Common;
@@ -269,8 +270,13 @@ namespace Jellyfin.Naming.Tests.Video
                 files.Select(i => VideoResolver.Resolve(i, false, _namingOptions)).OfType<VideoFileInfo>().ToList(),
                 _namingOptions).ToList();
 
-            Assert.Equal(7, result.Count);
-            Assert.Empty(result[0].AlternateVersions);
+            Assert.Single(result);
+            Assert.Equal(6, result[0].AlternateVersions.Count);
+
+            // Verify 3D recognition is preserved on alternate versions
+            var hsbs = result[0].AlternateVersions.First(v => v.Path.Contains("3d-hsbs", StringComparison.Ordinal));
+            Assert.True(hsbs.Is3D);
+            Assert.Equal("hsbs", hsbs.Format3D);
         }
 
         [Fact]
@@ -435,5 +441,39 @@ namespace Jellyfin.Naming.Tests.Video
 
             Assert.Empty(result);
         }
+
+        [Fact]
+        public void Resolve_GivenUnderscoreSeparator_GroupsVersions()
+        {
+            var files = new[]
+            {
+                "/movies/Movie (2020)/Movie (2020)_4K.mkv",
+                "/movies/Movie (2020)/Movie (2020)_1080p.mkv"
+            };
+
+            var result = VideoListResolver.Resolve(
+                files.Select(i => VideoResolver.Resolve(i, false, _namingOptions)).OfType<VideoFileInfo>().ToList(),
+                _namingOptions).ToList();
+
+            Assert.Single(result);
+            Assert.Single(result[0].AlternateVersions);
+        }
+
+        [Fact]
+        public void Resolve_GivenDotSeparator_GroupsVersions()
+        {
+            var files = new[]
+            {
+                "/movies/Movie (2020)/Movie (2020).UHD.mkv",
+                "/movies/Movie (2020)/Movie (2020).1080p.mkv"
+            };
+
+            var result = VideoListResolver.Resolve(
+                files.Select(i => VideoResolver.Resolve(i, false, _namingOptions)).OfType<VideoFileInfo>().ToList(),
+                _namingOptions).ToList();
+
+            Assert.Single(result);
+            Assert.Single(result[0].AlternateVersions);
+        }
     }
 }