feat(organize): organize arbitrary source dir (e.g. downloads) with dedup + 洗版

- Add OrganizeDirectory service: walk an arbitrary source directory (download
  dir / NAS direct-read path) and organize video files into the destination,
  without requiring the source to be a registered library.
- Dedup: skip media already present in the destination (matched by scanned DB
  identity title+year[/season+episode], robust to dir case/layout, plus a
  filesystem folder fallback).
- 洗版 (resolution replacement): when the source resolution is higher than the
  existing version, replace the lower-res file (+NFO sidecar +DB row). Prefers
  scanned dimensions, then ffprobe, then filename token; never replaces on
  unknown resolution.
- New endpoints: GET /admin/organize/sources (download/media dir candidates)
  and POST /admin/organize/source.
- UI: ToolsPage adds a '整理来源目录（去重+洗版）' form so operators can pick the
  download dir as the organize source.

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

internal/handler/organizer.go

@@ -63,3 +63,25 @@ func organizeLibraryHandler(svc *service.Container) gin.HandlerFunc {
 		c.JSON(http.StatusOK, res)
 	}
 }
+
+// organizeSourcesHandler lists selectable organize source directories (download
+// dir + media dir) so the UI can offer them alongside registered libraries.
+func organizeSourcesHandler(svc *service.Container) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{"sources": svc.Organizer.OrganizeSourceCandidates()})
+	}
+}
+
+// organizeDirectoryHandler organizes an arbitrary source directory (e.g. the
+// download directory) into the destination with dedup + 洗版.
+func organizeDirectoryHandler(svc *service.Container) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		opts := bindOrganizeOptions(c)
+		res, err := svc.Organizer.OrganizeDirectory(c.Request.Context(), opts)
+		if err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+			return
+		}
+		c.JSON(http.StatusOK, res)
+	}
+}