feat(storage): add S3/R2 abstraction with local Rustfs dev

- Add backend/internal/s3/ with build-tag pattern (dev vs prod)
- Dev: Uses local Rustfs container (S3-compatible)
- Prod: Stub for R2 Cloudflare (add AWS SDK to implement)
- Add S3 env vars to .env.example and .env
- Add Rustfs service to compose.yml
- Add Rustfs reset to local-dev-2.sh (wipes data on each run)

backend/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"crussell/auth"
 	"crussell/internal/dav"
+	"crussell/internal/s3"
 	"fmt"
 	"log"
 	"net/http"
@@ -46,9 +47,18 @@ func initDav() {
 	fmt.Println("DAV Service connected successfully")
 }
 
+func initS3() {
+	if err := s3.Connect(); err != nil {
+		log.Printf("WARNING: Failed to connect to S3: %v", err)
+	} else {
+		fmt.Println("S3 client initialized")
+	}
+}
+
 func main() {
 	initDB()
 	initDav()
+	initS3()
 
 	r := chi.NewRouter()