fix: add missing WebDAV path migration and remove duplicate migration.go

cmd/server/main.go

@@ -366,6 +366,41 @@ func migrateOldPaths(st *store.Store, dataDir string, logger *slog.Logger) {
 		}
 	}
 
+	// Migrate WebDAV files from old flat structure (dataDir/files/<username>/)
+	// to new nested structure (dataDir/<username>/files/)
+	filesRoot := filepath.Join(dataDir, "files")
+	if _, err := os.Stat(filesRoot); err == nil {
+		if entries, er := os.ReadDir(filesRoot); er == nil {
+			for _, entry := range entries {
+				if !entry.IsDir() {
+					continue
+				}
+				username := entry.Name()
+				oldWebdavPath := filepath.Join(filesRoot, username)
+				newUserDir := filepath.Join(dataDir, username)
+				newWebdavPath := filepath.Join(newUserDir, "files")
+
+				if _, e := os.Stat(oldWebdavPath); e != nil {
+					continue
+				}
+				if _, e := os.Stat(newWebdavPath); !os.IsNotExist(e) {
+					continue
+				}
+
+				logger.Info("Migrating webdav files", "user", username, "from", oldWebdavPath, "to", newWebdavPath)
+				if mkErr := os.MkdirAll(filepath.Dir(newWebdavPath), 0755); mkErr != nil {
+					logger.Warn("Failed to create directory for webdav migration", "path", newWebdavPath, "error", mkErr)
+					continue
+				}
+				if mvErr := moveDirContent(oldWebdavPath, newWebdavPath); mvErr != nil {
+					logger.Warn("Failed to migrate webdav files", "user", username, "error", mvErr)
+				} else {
+					logger.Info("webdav files migration complete", "user", username)
+				}
+			}
+		}
+	}
+
 	logger.Info("Legacy structure check complete")
 }