feat(strm): auto-append remote directory tail to local output path (#16)

When adding or editing a cloud sync path, append the last segment of the
remote directory to the local output directory (e.g. /home/ubuntu/strm + 电影).
Remote changes replace the previous auto-appended tail; local browse and blur
commit the base path with the current remote tail.

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

web/src/utils/strmPaths.ts

@@ -0,0 +1,53 @@
+/** 取路径最后一级目录/文件名（兼容 / 与 \\）。 */
+export function lastPathSegment(path: string): string {
+  const trimmed = path.trim().replace(/[\\/]+$/, '')
+  if (!trimmed) return ''
+  const parts = trimmed.split(/[/\\]/).filter(Boolean)
+  return parts[parts.length - 1] ?? ''
+}
+
+function pathSeparator(path: string): '/' | '\\' {
+  return path.includes('\\') ? '\\' : '/'
+}
+
+function normalizeSlashes(path: string): string {
+  return path.replace(/\\/g, '/').replace(/\/+$/, '')
+}
+
+/** 去掉 local 末尾与 prevRemoteTail 匹配的自动拼接段。 */
+function stripRemoteTail(localPath: string, prevRemoteTail: string): string {
+  if (!prevRemoteTail) return localPath.trim()
+  const trimmed = localPath.trim()
+  if (!trimmed) return ''
+  const norm = normalizeSlashes(trimmed)
+  const suffix = '/' + prevRemoteTail
+  if (norm.endsWith(suffix)) {
+    const stripped = norm.slice(0, -suffix.length)
+    if (!stripped) return ''
+    return stripped.split('/').join(pathSeparator(trimmed))
+  }
+  if (norm === prevRemoteTail) return ''
+  return trimmed
+}
+
+/** 将远端最后一级目录名拼到本地输出目录末尾；远端变更时替换旧尾段。 */
+export function syncLocalPathWithRemote(
+  localPath: string,
+  remotePath: string,
+  prevRemoteTail = '',
+): { localPath: string; remoteTail: string } {
+  const remoteTail = lastPathSegment(remotePath)
+  const base = stripRemoteTail(localPath, prevRemoteTail)
+  if (!remoteTail) {
+    return { localPath: base || localPath.trim(), remoteTail: '' }
+  }
+  if (!base) {
+    return { localPath: localPath.trim(), remoteTail }
+  }
+  const sep = pathSeparator(base)
+  const normBase = normalizeSlashes(base)
+  if (normBase.endsWith('/' + remoteTail)) {
+    return { localPath: base, remoteTail }
+  }
+  return { localPath: `${base}${sep}${remoteTail}`, remoteTail }
+}