[friction] ignore bin (#8952)

Agents love to create stuff in `bin` which we have to manually ignore.
The right thing to do is to git ignore the directory.



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Author: pq

.gitignore

@@ -21,6 +21,7 @@
 .vscode/
 .sandbox/
 artifacts/
+/bin/
 build/
 flutter-gui-tests/.gradle/
 flutter-gui-tests/guitest.log