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/scraper_write_metadata_files.go

@@ -38,9 +38,9 @@ func (s *ScraperService) writeMediaArtworkFilesAfterScrape(ctx context.Context,
 	if dir == "" || dir == "." {
 		return
 	}
-	// Scope sidecar names by the media file's base name (e.g. A.mp4 -> A-poster.jpg)
-	// so that multiple movies sharing one directory (A.mp4 + B.mp4) never clash.
-	base := strings.TrimSuffix(filepath.Base(refreshed.Path), filepath.Ext(refreshed.Path))
+	// Scope sidecar names by the shared media stem (e.g. A.mkv.strm / A.mp4.strm -> A-poster.jpg)
+	// so multi-version files in one folder share artwork and never diverge by container.
+	base := mediaSidecarBase(refreshed.Path)
 	if base == "" || base == "." {
 		return
 	}