feat(strm): 同名多版本择优 / keep_ext，并支持合并展示与播放切换 (#30)

* feat(strm): 同名多版本择优/keep_ext，并支持合并展示与播放切换

默认对同名不同扩展（如 .mkv/.mp4）按体积→mtime→扩展名优先级择优生成一条 strm，冲突打日志；开启 keep_ext 则分别生成 name.ext.strm。媒体详情与播放器可切换版本，列表继续合并同片多版本，Emby MediaSources 名称区分容器/分辨率。

Co-authored-by: truewhile <truewhile@users.noreply.github.com>

* fix(meta): 边车匹配忽略 .mkv.strm 中间扩展，同片共享 NFO/海报/字幕

NFO、海报、字幕与刮削写出统一使用 mediaSidecarBase 词干，使竞女01.mkv.strm
与竞女01.mp4.strm 配对同一套 竞女01.nfo / 竞女01-poster / 竞女01.srt；
仍兼容历史上的 name.mkv.nfo 命名。

Co-authored-by: truewhile <truewhile@users.noreply.github.com>

* fix(emby): People NFO 按共享词干匹配 keep_ext strm

resolveMediaPeople 改为查找竞女01.nfo（并兼容旧的竞女01.mkv.nfo），
同时修正把 decodeNFOFile 的 partial 误当 ok 导致完整 NFO 被跳过的问题。

Co-authored-by: truewhile <truewhile@users.noreply.github.com>

---------

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: truewhile <truewhile@users.noreply.github.com>

internal/service/organizer_sidecar.go

@@ -51,23 +51,25 @@ var artworkSidecarExtensions = []string{".jpg", ".jpeg", ".png", ".webp", ".gif"
 // behind in the old folder; this keeps artwork with the organized file.
 func transferSidecarArtwork(srcMedia, dstMedia string, mode TransferMode) error {
 	srcDir := filepath.Dir(srcMedia)
-	base := strings.TrimSuffix(filepath.Base(srcMedia), filepath.Ext(srcMedia))
-	if base == "" || base == "." {
+	bases := mediaSidecarBaseVariants(srcMedia)
+	if len(bases) == 0 {
 		return nil
 	}
 	// Find every existing sidecar by probing suffix + extension combinations.
-	sources := make([]string, 0, len(artworkSidecarSuffixes)*len(artworkSidecarExtensions))
+	sources := make([]string, 0, len(artworkSidecarSuffixes)*len(artworkSidecarExtensions)*len(bases))
 	seen := map[string]struct{}{}
-	for _, suffix := range artworkSidecarSuffixes {
-		for _, ext := range artworkSidecarExtensions {
-			path := filepath.Join(srcDir, base+suffix+ext)
-			key := strings.ToLower(filepath.Clean(path))
-			if _, ok := seen[key]; ok {
-				continue
-			}
-			seen[key] = struct{}{}
-			if _, err := os.Stat(path); err == nil {
-				sources = append(sources, path)
+	for _, base := range bases {
+		for _, suffix := range artworkSidecarSuffixes {
+			for _, ext := range artworkSidecarExtensions {
+				path := filepath.Join(srcDir, base+suffix+ext)
+				key := strings.ToLower(filepath.Clean(path))
+				if _, ok := seen[key]; ok {
+					continue
+				}
+				seen[key] = struct{}{}
+				if _, err := os.Stat(path); err == nil {
+					sources = append(sources, path)
+				}
 			}
 		}
 	}
@@ -78,15 +80,36 @@ func transferSidecarArtwork(srcMedia, dstMedia string, mode TransferMode) error
 	if err := os.MkdirAll(dstDir, 0o755); err != nil { // #nosec G301 -- sidecar media directories must remain readable by NAS/player users.
 		return err
 	}
-	var firstErr error
+	dstBase := mediaSidecarBase(dstMedia)
+	if dstBase == "" {
+		dstBase = strings.TrimSuffix(filepath.Base(dstMedia), filepath.Ext(dstMedia))
+	}
 	for _, src := range sources {
-		dst := filepath.Join(dstDir, filepath.Base(src))
-		if _, err := os.Stat(dst); err == nil {
-			continue // never clobber an existing artwork at the destination
+		name := filepath.Base(src)
+		// Remap any legacy "Title.mkv-poster.jpg" onto the shared destination stem.
+		suffix := ""
+		lowerName := strings.ToLower(name)
+		for _, base := range bases {
+			prefix := strings.ToLower(base)
+			if strings.HasPrefix(lowerName, prefix) {
+				suffix = name[len(base):]
+				break
+			}
 		}
-		if err := transferFile(src, dst, mode); err != nil && firstErr == nil {
-			firstErr = err
+		dstName := name
+		if suffix != "" && dstBase != "" {
+			dstName = dstBase + suffix
+		}
+		dst := filepath.Join(dstDir, dstName)
+		if strings.EqualFold(filepath.Clean(src), filepath.Clean(dst)) {
+			continue
+		}
+		if _, err := os.Stat(dst); err == nil {
+			continue
+		}
+		if err := transferFile(src, dst, mode); err != nil {
+			return err
 		}
 	}
-	return firstErr
+	return nil
 }