feat(spotify): Connect-Spotify settings card (config + OAuth login + status) [S4.4]

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/composables/useSpotifySettings.ts

@@ -0,0 +1,48 @@
+export interface SpotifyConfigForm {
+  enabled: boolean;
+  backend: "auto" | "go-librespot" | "librespot";
+  clientId: string;
+  clientSecret: string; // blank means "unchanged"
+  deviceName: string;
+  bitrate: number;
+}
+
+export interface SpotifyStatus {
+  authorized: boolean;
+  backend: string;
+  deviceName: string;
+  binaryAvailable: boolean;
+}
+
+// 实验性 · 灰色地带 · 需要 Premium · 使用你自己的开发者应用凭据
+export const SPOTIFY_DISCLAIMER =
+  "实验性功能：通过 librespot 播放 Spotify 需要 Spotify Premium 账号，并使用你自己注册的 Spotify 开发者应用凭据。" +
+  "该方式处于 Spotify 服务条款的灰色地带，风险自负；默认关闭，不会内置任何共享凭据。";
+
+export function buildSpotifyPayload(f: SpotifyConfigForm): { spotify: Record<string, unknown> } {
+  const spotify: Record<string, unknown> = {
+    enabled: f.enabled,
+    backend: f.backend,
+    clientId: f.clientId,
+    deviceName: f.deviceName,
+    bitrate: f.bitrate,
+  };
+  if (f.clientSecret && f.clientSecret.length > 0) spotify.clientSecret = f.clientSecret;
+  return { spotify };
+}
+
+export function parseSpotifyRedirect(search: string): "success" | "error" | null {
+  const v = new URLSearchParams(search).get("spotify");
+  return v === "success" || v === "error" ? v : null;
+}
+
+export function statusSummary(
+  s: SpotifyStatus | null,
+  enabled: boolean,
+): { label: string; tone: "ok" | "warn" | "off" } {
+  if (!enabled) return { label: "已关闭", tone: "off" };
+  if (!s) return { label: "未知", tone: "warn" };
+  if (!s.binaryAvailable) return { label: "未检测到 librespot 可执行文件", tone: "warn" };
+  if (!s.authorized) return { label: "未授权（点击“连接 Spotify”登录）", tone: "warn" };
+  return { label: `已就绪 · 后端 ${s.backend}`, tone: "ok" };
+}