chore: drop an unrelated .gitignore line from this branch

The .gstack/ entry was created by local tooling during QA on this branch and got
swept in by a broad stage. It is unrelated to the file-type work and the repo
references .gstack nowhere, so it does not belong in this PR.

Author: mzxchandra

.gitignore

@@ -111,4 +111,3 @@ __pycache__/
 # `apps/sim/lib/uploads/` — 61 files of tracked source — and silently ignore
 # anything added there later.
 /uploads
-.gstack/