feat(video): link and stream Immich videos in the journey gallery

Immich timeline and album listings no longer filter out videos; each asset now carries its media type, which the provider picker forwards when linking. A linked video streams through Immich's transcoded /video/playback endpoint, and the asset proxy forwards the viewer's Range header (and passes 206/Content-Range back) so the player can seek. Synology video stays excluded until its stream API is verified.

Adds media_type/media_types to the provider-photos request contract.

shared/src/journey/journey.schema.ts

@@ -42,6 +42,9 @@ export const journeyProviderPhotosRequestSchema = z.object({
   asset_ids: z.array(z.union([z.string(), z.number()])).optional(),
   caption: z.string().optional(),
   passphrase: z.string().optional(),
+  // Per-asset 'image' | 'video' discriminator, parallel to asset_ids (#823).
+  media_type: z.string().optional(),
+  media_types: z.array(z.string()).optional(),
 });
 export type JourneyProviderPhotosRequest = z.infer<typeof journeyProviderPhotosRequestSchema>;