fix(playlists): better M3U paths matching across different UTF representations (#4890)

* fix: improve playlist path normalization for cross-platform compatibility

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: log normalized path when playlist path is not found

Signed-off-by: Deluan <deluan@navidrome.org>

* test: enhance Unicode normalization tests for playlist paths

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: enhance playlist path normalization for cross-platform compatibility

See https://github.com/navidrome/navidrome/pull/4789#issuecomment-3645724780

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: improve playlist path normalization to handle fullwidth characters and enhance cross-platform compatibility

Signed-off-by: Deluan <deluan@navidrome.org>

* formatting

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: adjust chunk size for M3U parsing to optimize SQLite expression tree depth

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>

persistence/mediafile_repository_test.go

@@ -561,4 +561,92 @@ var _ = Describe("MediaRepository", func() {
 			})
 		})
 	})
+
+	Describe("FindByPaths", func() {
+		// Test fixtures for Unicode and case-sensitivity tests
+		var testFiles []model.MediaFile
+
+		BeforeEach(func() {
+			testFiles = []model.MediaFile{
+				{ID: "findpath-1", LibraryID: 1, Path: "artist/Album/track.mp3", Title: "Track"},
+				{ID: "findpath-2", LibraryID: 1, Path: "artist/Album/UPPER.mp3", Title: "Upper"},
+				// Fullwidth uppercase: ＡＣＲＯＳＳ (U+FF21 U+FF23 U+FF32 U+FF2F U+FF33 U+FF33)
+				{ID: "findpath-3", LibraryID: 1, Path: "plex/02 - ＡＣＲＯＳＳ.flac", Title: "Fullwidth"},
+				// French diacritic: è (U+00E8, can decompose to e + combining grave)
+				{ID: "findpath-4", LibraryID: 1, Path: "artist/Michèle/song.mp3", Title: "French"},
+			}
+			for _, mf := range testFiles {
+				Expect(mr.Put(&mf)).To(Succeed())
+			}
+		})
+
+		AfterEach(func() {
+			for _, mf := range testFiles {
+				_ = mr.Delete(mf.ID)
+			}
+		})
+
+		It("finds files by exact path", func() {
+			results, err := mr.FindByPaths([]string{"1:artist/Album/track.mp3"})
+			Expect(err).ToNot(HaveOccurred())
+			Expect(results).To(HaveLen(1))
+			Expect(results[0].ID).To(Equal("findpath-1"))
+		})
+
+		It("finds files case-insensitively for ASCII characters (NOCASE)", func() {
+			// SQLite's COLLATE NOCASE handles ASCII case-insensitivity
+			results, err := mr.FindByPaths([]string{"1:ARTIST/ALBUM/TRACK.MP3"})
+			Expect(err).ToNot(HaveOccurred())
+			Expect(results).To(HaveLen(1))
+			Expect(results[0].ID).To(Equal("findpath-1"))
+		})
+
+		It("finds fullwidth characters only with exact case match (SQLite NOCASE limitation)", func() {
+			// SQLite's NOCASE does NOT handle fullwidth uppercase/lowercase equivalence
+			// The DB has fullwidth uppercase ＡＣＲＯＳＳ, searching with exact match should work
+			results, err := mr.FindByPaths([]string{"1:plex/02 - ＡＣＲＯＳＳ.flac"})
+			Expect(err).ToNot(HaveOccurred())
+			Expect(results).To(HaveLen(1))
+			Expect(results[0].ID).To(Equal("findpath-3"))
+
+			// Searching with fullwidth lowercase ａｃｒｏｓｓ should NOT match
+			// (this is the SQLite limitation that requires exact matching for non-ASCII)
+			results, err = mr.FindByPaths([]string{"1:plex/02 - ａｃｒｏｓｓ.flac"})
+			Expect(err).ToNot(HaveOccurred())
+			Expect(results).To(BeEmpty())
+		})
+
+		It("returns multiple files when querying multiple paths", func() {
+			results, err := mr.FindByPaths([]string{
+				"1:artist/Album/track.mp3",
+				"1:artist/Album/UPPER.mp3",
+			})
+			Expect(err).ToNot(HaveOccurred())
+			Expect(results).To(HaveLen(2))
+		})
+
+		It("returns empty slice for non-existent paths", func() {
+			results, err := mr.FindByPaths([]string{"1:nonexistent/path.mp3"})
+			Expect(err).ToNot(HaveOccurred())
+			Expect(results).To(BeEmpty())
+		})
+
+		It("returns empty slice for empty input", func() {
+			results, err := mr.FindByPaths([]string{})
+			Expect(err).ToNot(HaveOccurred())
+			Expect(results).To(BeEmpty())
+		})
+
+		It("handles library-qualified paths correctly", func() {
+			// Library 1 should find the file
+			results, err := mr.FindByPaths([]string{"1:artist/Album/track.mp3"})
+			Expect(err).ToNot(HaveOccurred())
+			Expect(results).To(HaveLen(1))
+
+			// Library 2 should NOT find it (file is in library 1)
+			results, err = mr.FindByPaths([]string{"2:artist/Album/track.mp3"})
+			Expect(err).ToNot(HaveOccurred())
+			Expect(results).To(BeEmpty())
+		})
+	})
 })