feat(oauth): import favoris/abos Google (YouTube) et Twitch vers abonnements/likes

- Backend: server/oauth.mjs (auth URL, echange code, refresh, fetch
  subscriptions/likes Google, follows Twitch), table oauth_connections
  + migration, routes /api/oauth/:provider/{url,callback,preview,import},
  /api/oauth/{status,connections}
- Front: /library/import (connect, preview, import), service
  oauth-import, lien depuis Abonnements
- Config: GOOGLE_CLIENT_ID/SECRET/REDIRECT_URI, TWITCH_REDIRECT_URI,
  OAUTH_APP_BASE_URL documentes (.env.example, docker-compose),
  passthrough docker-compose.local.yml, roadmap README cochee

src/services/oauth-import.service.ts

@@ -0,0 +1,62 @@
+import { Injectable, inject } from '@angular/core';
+import { HttpClient } from '@angular/common/http';
+import { Observable } from 'rxjs';
+
+export interface OAuthConnection {
+  provider: string;
+  externalUserId: string | null;
+  displayName: string | null;
+  avatarUrl: string | null;
+  scopes: string | null;
+  expiresAt: number | null;
+  connectedAt: number | null;
+  updatedAt: number | null;
+}
+
+export interface OAuthPreview {
+  provider: string;
+  subscriptions: Array<{ provider: string; externalId: string; title: string; handle?: string | null; avatarUrl?: string | null; url?: string | null }>;
+  likes: Array<{ provider: string; videoId: string; title: string; thumbnail?: string }>;
+  subscriptionCount: number;
+  likeCount: number;
+}
+
+export interface OAuthImportResult {
+  provider: string;
+  importedSubscriptions: number;
+  importedLikes: number;
+  skippedSubscriptions: number;
+  skippedLikes: number;
+}
+
+@Injectable({ providedIn: 'root' })
+export class OAuthImportService {
+  private http = inject(HttpClient);
+
+  status(): Observable<{ google: { configured: boolean; missing: string[] }; twitch: { configured: boolean; missing: string[] } }> {
+    return this.http.get<any>('/api/oauth/status');
+  }
+
+  connections(): Observable<{ connections: OAuthConnection[]; status: any }> {
+    return this.http.get<any>('/api/oauth/connections');
+  }
+
+  async connect(provider: 'google' | 'twitch'): Promise<void> {
+    const res: any = await this.http.get(`/api/oauth/${provider}/url`).toPromise().catch((e) => { throw e; });
+    const url = res?.url;
+    if (!url) throw new Error('oauth_url_failed');
+    window.location.href = url;
+  }
+
+  disconnect(provider: string): Observable<void> {
+    return this.http.delete<void>(`/api/oauth/${provider}`);
+  }
+
+  preview(provider: string): Observable<OAuthPreview> {
+    return this.http.get<OAuthPreview>(`/api/oauth/${provider}/preview`);
+  }
+
+  importAll(provider: string, types: string[]): Observable<OAuthImportResult> {
+    return this.http.post<OAuthImportResult>(`/api/oauth/${provider}/import`, { types });
+  }
+}