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>

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

internal/service/subtitle.go

@@ -142,7 +142,10 @@ func (s *SubtitleService) discoverUncached(ctx context.Context, mediaID string)
 		return nil, errors.New("media not found")
 	}
 	dir := filepath.Dir(m.Path)
-	base := strings.TrimSuffix(filepath.Base(m.Path), filepath.Ext(m.Path))
+	bases := mediaSidecarBaseVariants(m.Path)
+	if len(bases) == 0 {
+		bases = []string{strings.TrimSuffix(filepath.Base(m.Path), filepath.Ext(m.Path))}
+	}
 
 	candidates := make([]string, 0, 16)
 	candidates = append(candidates, dir)
@@ -166,13 +169,23 @@ func (s *SubtitleService) discoverUncached(ctx context.Context, mediaID string)
 				continue
 			}
 			fullName := strings.TrimSuffix(e.Name(), ext)
-			if !strings.HasPrefix(strings.ToLower(fullName), strings.ToLower(base)) &&
-				c == dir {
-				// In the same directory we require a basename match;
-				// inside subs/ subdirs we accept anything.
-				continue
+			matchedBase := ""
+			if c == dir {
+				for _, base := range bases {
+					if strings.HasPrefix(strings.ToLower(fullName), strings.ToLower(base)) {
+						matchedBase = base
+						break
+					}
+				}
+				if matchedBase == "" {
+					// In the same directory we require a basename match;
+					// inside subs/ subdirs we accept anything.
+					continue
+				}
+			} else if len(bases) > 0 {
+				matchedBase = bases[0]
 			}
-			lang := detectLang(fullName, base)
+			lang := detectLang(fullName, matchedBase)
 			tracks = append(tracks, SubtitleTrack{
 				Lang:  lang,
 				Label: lang,