Add common build output directories to .gitignore

This commit updates the `app/.gitignore` file to include several standard build and release output directories. The following directories will now be ignored by Git:

- `/release`
- `/prod`
- `/beta`
- `/alpha`
- `/nightly`
- `/tmp`

Author: CreativeCodeCat

app/.gitignore

@@ -1 +1,7 @@
-/build
+/build
+/release
+/prod
+/beta
+/alpha
+/nightly
+/tmp