feat(emby): support multiple connection lines for remote mount (#9)

Add account-level multi-line configuration for emby_remote mounts.
Lines are stored in strm_accounts.config as a urls JSON array with
backward compatibility for the legacy single url field. The backend
automatically fails over to the next line on connection errors and
persists the working active_line index.

Frontend: multi-line editor on Emby mount page and STRM account dialog
with add/remove/reorder, line names, and URL validation.

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

web/src/utils/embyRemoteLines.ts

@@ -0,0 +1,31 @@
+export type EmbyRemoteLine = {
+  name: string
+  url: string
+}
+
+export function normalizeEmbyRemoteLines(lines: EmbyRemoteLine[]): EmbyRemoteLine[] {
+  return lines
+    .map((line) => ({
+      name: line.name.trim(),
+      url: line.url.trim().replace(/\/+$/, ''),
+    }))
+    .filter((line) => line.url.startsWith('http://') || line.url.startsWith('https://'))
+}
+
+export function encodeEmbyRemoteConfigLines(lines: EmbyRemoteLine[]): Record<string, string> {
+  const normalized = normalizeEmbyRemoteLines(lines)
+  if (normalized.length === 0) {
+    return {}
+  }
+  return {
+    urls: JSON.stringify(normalized),
+    url: normalized[0].url,
+  }
+}
+
+export function defaultEmbyRemoteLines(existing?: EmbyRemoteLine[]): EmbyRemoteLine[] {
+  if (existing && existing.length > 0) {
+    return existing.map((line) => ({ name: line.name ?? '', url: line.url ?? '' }))
+  }
+  return [{ name: '线路 1', url: '' }]
+}