tests: Cover document export reply formats

Exercise existing files, directories and nonexistent files against a real
document portal on the private test bus. Verify that --noexist returns a
usable export after the origin is created and preserves its read grant.

The regression fails on the AddNamed reply type mismatch without the fix.
All four checks pass with it.
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Gitea Version: 1.28.0+dev-477-g8b6ad49a5f