feat(channel): identite chaine partagee cliquable partout + logos fiabilises

- Nouveau app-channel-identity (avatar+nom -> /channel, fallback resolve /api/channels, initiales sinon)
- ProviderBadge: accepte les ids courts yt/dm/tw/pt/od/ru
- Search adapters yt/dm/pt/od: conservent channelExternalId/channelAvatarUrl (pt derive instance|channel)
- video-card/themes/watch/related/suggestions/subscriptions/channel-header uniformises sur l'identite partagee

src/app/shared/components/video-card/video-card.component.ts

@@ -5,6 +5,7 @@ import { RouterLink } from '@angular/router';
 import { DurationPipe } from '../../pipes/duration.pipe';
 import { ProviderBadgeComponent } from '../provider-badge/provider-badge.component';
 import { SubscribeButtonComponent } from '../subscribe-button/subscribe-button.component';
+import { ChannelIdentityComponent } from '../channel-identity/channel-identity.component';
 import type { ChannelMeta, ProviderId } from '../../models/channel.model';
 
 @Component({
@@ -12,7 +13,7 @@ import type { ChannelMeta, ProviderId } from '../../models/channel.model';
   templateUrl: './video-card.component.html',
   styleUrls: ['./video-card.component.scss'],
   standalone: true,
-  imports: [CommonModule, RouterLink, DurationPipe, ProviderBadgeComponent, SubscribeButtonComponent],
+  imports: [CommonModule, RouterLink, DurationPipe, ProviderBadgeComponent, SubscribeButtonComponent, ChannelIdentityComponent],
 })
 export class VideoCardComponent {
   @Input() video!: VideoItem;
@@ -52,8 +53,7 @@ export class VideoCardComponent {
     return (channel?.externalId || '').trim();
   }
 
-  channelInitial(channel?: ChannelMeta | null, fallback?: string | null): string {
-    const name = this.channelDisplayName(channel, fallback);
-    return name ? name.charAt(0).toUpperCase() : 'C';
+  get showSubscribe(): boolean {
+    return Boolean(this.video.channelMeta && this.channelProviderId && this.channelExternalId());
   }
 }