feat(storage): add S3 backend support and advanced upload limits

- Introduce S3-compatible storage backend support using minio-go.
- Add configuration options for local storage limits, box limits, and rate limiting.
- Implement storage backend selection (local vs S3) for anonymous and registered users.
- Add an `/admin/storage` management interface.
- Update documentation and environment examples with the new configuration variables.

.env.example

@@ -16,6 +16,17 @@ WARPBOX_ANONYMOUS_DAILY_UPLOAD_MB=2048
 WARPBOX_USER_DAILY_UPLOAD_MB=8192
 WARPBOX_DEFAULT_USER_STORAGE_MB=51200
 WARPBOX_USAGE_RETENTION_DAYS=30
+WARPBOX_LOCAL_STORAGE_MAX_GB=100
+WARPBOX_ANONYMOUS_MAX_DAYS=30
+WARPBOX_USER_MAX_DAYS=90
+WARPBOX_ANONYMOUS_DAILY_BOXES=100
+WARPBOX_USER_DAILY_BOXES=250
+WARPBOX_ANONYMOUS_ACTIVE_BOXES=500
+WARPBOX_USER_ACTIVE_BOXES=1000
+WARPBOX_SHORT_WINDOW_REQUESTS=60
+WARPBOX_SHORT_WINDOW_SECONDS=60
+WARPBOX_ANONYMOUS_STORAGE_BACKEND=local
+WARPBOX_USER_STORAGE_BACKEND=local
 WARPBOX_READ_TIMEOUT=15s
 WARPBOX_WRITE_TIMEOUT=60s
 WARPBOX_IDLE_TIMEOUT=120s