fix: yarnv4 requires shebangs in shell scripts to allow execution

.dockerignore

@@ -14,3 +14,4 @@ frontend/node_modules
 !.yarn/**
 !.yarnrc.yml
 !frontend/.yarn/**
+node_modules

frontend/.yarnrc.yml

@@ -1 +1,2 @@
 yarnPath: .yarn/releases/yarn-4.2.2.cjs
+nodeLinker: node-modules

frontend/check-imports.rc

@@ -1,3 +1,4 @@
+#!/usr/bin/env sh
 if grep -R --include="*.js" --include="*.jsx" --include="*.ts" --include="*.tsx" "from '@mui/icons-material'" src; then
   echo "Prohibited import from '@mui/icons-material' found. Use default imports referencing the file instead of the 
   global package. Example: import Delete from '@mui/icons-material/Delete';'"

scripts/build-frontend-if-needed.sh

@@ -1,4 +1,4 @@
 #!/usr/bin/env sh
 if [ ! -d ./frontend/build ]; then
-    yarn --cwd ./frontend install --immutable && yarn build:frontend;
+    yarn --cwd ./frontend install --immutable && echo "Done installing" && yarn build:frontend;
 fi