feat: integrate MinIO for video storage, add video routes, and update README with API documentation

Backend/README.md

@@ -21,6 +21,14 @@ DATABASE_URL=postgres://username:password@localhost:5432/database_name
 JWT_SECRET=replace_with_a_long_random_secret
 JWT_EXPIRES_IN=7d
 PORT=3000
+MINIO_ENDPOINT=localhost
+MINIO_PORT=9000
+MINIO_USE_SSL=false
+MINIO_ACCESS_KEY=minioadmin
+MINIO_SECRET_KEY=minioadmin
+MINIO_BUCKET=videos
+MINIO_REGION=us-east-1
+MINIO_PRESIGNED_EXPIRY_SECONDS=600
 ```
 
 ## Run app
@@ -78,3 +86,41 @@ Get current user:
 GET /auth/me
 Authorization: Bearer <token>
 ```
+
+## Video API (Dummy MinIO S3 Integration)
+
+All routes require a JWT Bearer token.
+
+Create a presigned upload URL:
+
+```bash
+POST /videos/upload-url
+Authorization: Bearer <token>
+{
+  "fileName": "sample.mp4",
+  "prefix": "raw"
+}
+```
+
+Get a presigned download URL:
+
+```bash
+GET /videos/download-url?objectKey=raw/<user-id>/<timestamp>-sample.mp4
+Authorization: Bearer <token>
+```
+
+List video objects:
+
+```bash
+GET /videos?prefix=raw&limit=20
+Authorization: Bearer <token>
+```
+
+Delete a video object:
+
+```bash
+DELETE /videos?objectKey=raw/<user-id>/<timestamp>-sample.mp4
+Authorization: Bearer <token>
+```
+
+**Self-hosted MinIO note** Make sure the backend can reach your MinIO endpoint (network, TLS, credentials) and mirror any bucket changes you make outside of the app in `MINIO_BUCKET`, otherwise uploads/downloads fail.