Crack: bypass license check - force all limits unlimited

- Vendor shuffle-shared v1.2.51 as backend/go-app/shuffle-shared
- Add replace directive in go.mod to use the local moduled copy
- In HandleCheckLicense, force org.Licensed=true and set every
  SyncFeatures limit to 1e9, skipping all license-key logic
- Update Dockerfile to ADD the local shuffle-shared before go build
- Verified: backend image builds successfully via docker

backend/go-app/go.mod

@@ -2,7 +2,7 @@ module shuffle
 
 go 1.25.0
 
-//replace github.com/shuffle/shuffle-shared => ../../../shuffle-shared
+replace github.com/shuffle/shuffle-shared => ./shuffle-shared
 
 //replace github.com/frikky/schemaless => ../../../schemaless