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.

backend/go.mod

@@ -3,9 +3,28 @@ module warpbox.dev/backend
 go 1.26
 
 require (
+	github.com/minio/minio-go/v7 v7.2.0
 	go.etcd.io/bbolt v1.4.3
-	golang.org/x/crypto v0.33.0
+	golang.org/x/crypto v0.51.0
 	golang.org/x/image v0.41.0
 )
 
-require golang.org/x/sys v0.30.0 // indirect
+require (
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/klauspost/compress v1.18.6 // indirect
+	github.com/klauspost/cpuid/v2 v2.2.11 // indirect
+	github.com/klauspost/crc32 v1.3.0 // indirect
+	github.com/minio/crc64nvme v1.1.1 // indirect
+	github.com/minio/md5-simd v1.1.2 // indirect
+	github.com/philhofer/fwd v1.2.0 // indirect
+	github.com/rs/xid v1.6.0 // indirect
+	github.com/tinylib/msgp v1.6.1 // indirect
+	github.com/zeebo/xxh3 v1.1.0 // indirect
+	go.yaml.in/yaml/v3 v3.0.4 // indirect
+	golang.org/x/net v0.53.0 // indirect
+	golang.org/x/sys v0.44.0 // indirect
+	golang.org/x/text v0.37.0 // indirect
+	gopkg.in/ini.v1 v1.67.2 // indirect
+)