refactor: backend-authoritative team scope and config/input hardening

donut-sync/.env.example

@@ -1,9 +1,15 @@
-SYNC_TOKEN=secret-sync-token
+# REQUIRED: a long, random shared secret used to authenticate sync clients.
+# Generate one, e.g.:  openssl rand -hex 32
+# The server refuses to start with this placeholder or a value shorter than 24 chars.
+SYNC_TOKEN=CHANGE_ME_generate_a_long_random_secret
 
 PORT=12342
+
+# REQUIRED S3 / S3-compatible (e.g. MinIO) connection. No defaults are assumed —
+# the server fails to start if endpoint / access key / secret key is missing.
 S3_ENDPOINT=http://localhost:8987
 S3_REGION=us-east-1
-S3_ACCESS_KEY_ID=minioadmin
-S3_SECRET_ACCESS_KEY=minioadmin
+S3_ACCESS_KEY_ID=CHANGE_ME
+S3_SECRET_ACCESS_KEY=CHANGE_ME
 S3_BUCKET=donut-sync
 S3_FORCE_PATH_STYLE=true