Change frontend .env files to be committed and have .env.*.local overrides (#6207)

frontend/.gitignore

@@ -14,14 +14,13 @@
 
 # misc
 .DS_Store
-.env
-.env.saas
-.env.desktop
 .env.local
-.env.development.local
-.env.test.local
-.env.production.local
-!.env*.example
+.env.*.local
+
+# Root .gitignore ignores all .env* - whitelist our committed ones here
+!.env
+!.env.desktop
+!.env.saas
 
 npm-debug.log*
 yarn-debug.log*
@@ -32,4 +31,4 @@ test-results
 
 # auto-generated files
 /src/assets/material-symbols-icons.json
-/src/assets/material-symbols-icons.d.ts
+/src/assets/material-symbols-icons.d.ts