fix(scanner): handle cross-library relative paths in playlists (#4659)

* fix: handle cross-library relative paths in playlists

Playlists can now reference songs in other libraries using relative paths.
Previously, relative paths like '../Songs/abc.mp3' would not resolve correctly
when pointing to files in a different library than the playlist file.

The fix resolves relative paths to absolute paths first, then checks which
library they belong to using the library regex. This allows playlists to
reference files across library boundaries while maintaining backward
compatibility with existing single-library relative paths.

Fixes #4617

* fix: enhance playlist path normalization for cross-library support

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

* refactor: improve handling of relative paths in playlists for cross-library compatibility

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

* fix: ensure longest library path matches first to resolve prefix conflicts in playlists

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

* test: refactor tests isolation

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

* fix: enhance handling of library-qualified paths and improve cross-library playlist support

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

* refactor: simplify mocks

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

* fix: lint

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

* fix: improve path resolution for cross-library playlists and enhance error handling

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

* refactor

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

* refactor: remove unnecessary path validation fallback

Remove validatePathInLibrary function and its fallback logic in
resolveRelativePath. The library matcher should always find the correct
library, including the playlist's own library. If this fails, we now
return an invalid resolution instead of attempting a fallback validation.

This simplifies the code by removing redundant validation logic that
was masking test setup issues. Also fixes test mock configuration to
properly set up library paths that match folder LibraryPath values.

* refactor: consolidate path resolution logic

Collapse resolveRelativePath and resolveAbsolutePath into a unified
resolvePath function, extracting common library matching logic into a
new findInLibraries helper method.

This eliminates duplicate code (~20 lines) while maintaining clear
separation of concerns: resolvePath handles path normalization
(relative vs absolute), and findInLibraries handles library matching.

Update tests to call resolvePath directly with appropriate parameters,
maintaining full test coverage for both absolute and relative path
scenarios.

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

* docs: add FindByPaths comment

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

* fix: enhance Unicode normalization for path comparisons in playlists. Fixes 4663

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

---------

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

persistence/mediafile_repository.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"fmt"
 	"slices"
+	"strconv"
+	"strings"
 	"sync"
 	"time"
 
@@ -193,12 +195,43 @@ func (r *mediaFileRepository) GetCursor(options ...model.QueryOptions) (model.Me
 	}, nil
 }
 
+// FindByPaths finds media files by their paths.
+// The paths can be library-qualified (format: "libraryID:path") or unqualified ("path").
+// Library-qualified paths search within the specified library, while unqualified paths
+// search across all libraries for backward compatibility.
 func (r *mediaFileRepository) FindByPaths(paths []string) (model.MediaFiles, error) {
-	sel := r.newSelect().Columns("*").Where(Eq{"path collate nocase": paths})
+	query := Or{}
+
+	for _, path := range paths {
+		parts := strings.SplitN(path, ":", 2)
+		if len(parts) == 2 {
+			// Library-qualified path: "libraryID:path"
+			libraryID, err := strconv.Atoi(parts[0])
+			if err != nil {
+				// Invalid format, skip
+				continue
+			}
+			relativePath := parts[1]
+			query = append(query, And{
+				Eq{"path collate nocase": relativePath},
+				Eq{"library_id": libraryID},
+			})
+		} else {
+			// Unqualified path: search across all libraries
+			query = append(query, Eq{"path collate nocase": path})
+		}
+	}
+
+	if len(query) == 0 {
+		return model.MediaFiles{}, nil
+	}
+
+	sel := r.newSelect().Columns("*").Where(query)
 	var res dbMediaFiles
 	if err := r.queryAll(sel, &res); err != nil {
 		return nil, err
 	}
+
 	return res.toModels(), nil
 }