feat: add video upload feature with support for validation and processing

- Introduced "video" as a new content type across backend and frontend.
- Updated validation schemas and MIME-type handling for video files.
- Implemented file size limits for videos (10 MB max) in configuration.
- Enhanced upload flow with auto-detection of file types (image, GIF, video).
- Expanded media processing to handle video files and convert them to WebM format.

backend/src/config/env.schema.ts

@@ -48,6 +48,7 @@ export const envSchema = z.object({
 	// Media Limits
 	MAX_IMAGE_SIZE_KB: z.coerce.number().default(512),
 	MAX_GIF_SIZE_KB: z.coerce.number().default(1024),
+	MAX_VIDEO_SIZE_KB: z.coerce.number().default(10240),
 });
 
 export type Env = z.infer<typeof envSchema>;