feat: add S3/SigV4 proxy handler for MinIO JWT auth

- New s3/sigv4.go: JWT → SigV4 converter proxy
  * Validates JWT via JWKS
  * Checks s3:read/s3:write permissions
  * Forwards requests to MinIO with SigV4 signature
- Router: Add /v1/s3/* routing to S3Handler
- Gateway main: Initialize S3Handler with MinIO credentials
- Proxy: Add JWTValidator() getter for s3 handler
- Env vars: MINIO_ENDPOINT, MINIO_ACCESS_KEY, MINIO_SECRET_KEY

go.mod

@@ -22,14 +22,18 @@ require (
 	github.com/facebookgo/clock v0.0.0-20150410010913-600d898af40a // indirect
 	github.com/go-logr/logr v1.4.4 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/go-resty/resty/v2 v2.17.2 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/golang/mock v1.6.0 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/grpc-ecosystem/go-grpc-middleware/v2 v2.3.2 // indirect
 	github.com/grpc-ecosystem/grpc-gateway/v2 v2.30.0 // indirect
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/nexus-rpc/nexus-proto-annotations v0.1.0 // indirect
 	github.com/nexus-rpc/sdk-go v0.7.0 // indirect
 	github.com/robfig/cron v1.2.0 // indirect
+	github.com/spf13/cobra v1.10.2 // indirect
+	github.com/spf13/pflag v1.0.10 // indirect
 	github.com/stretchr/objx v0.5.3 // indirect
 	github.com/stretchr/testify v1.12.1 // indirect
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
@@ -41,7 +45,7 @@ require (
 	golang.org/x/sync v0.22.0 // indirect
 	golang.org/x/sys v0.47.0 // indirect
 	golang.org/x/text v0.41.0 // indirect
-	golang.org/x/time v0.3.0 // indirect
+	golang.org/x/time v0.12.0 // indirect
 	google.golang.org/genproto/googleapis/api v0.0.0-20260819154853-08b0e4226688 // indirect
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20260819154853-08b0e4226688 // indirect
 )