Please consider reducing broad default Flatpak permissions

The current manifest grants `--filesystem=host` and `--filesystem=/tmp` by default. For a Markdown editor, this seems broader than necessary, since opening and saving user-selected files normally handled through portals such as `xdg-documents` or `--filesystem=home` is enough.

https://github.com/flathub/com.github.marktext.marktext/blob/e58dab924e2981bae202ae6ecfe5e5a30c78dbda/com.github.marktext.marktext.json#L18

Could maintainers clarify which current MarkText features require full host filesystem access and direct host `/tmp` access by default?

I also noticed Secret Service/keyring access via `--talk-name=org.freedesktop.secrets` and `--filesystem=xdg-run/keyring`. The desktop source imports `keytar`, but I could not find an active encrypted setting in the current data center schema, so it would be helpful to know which user-facing feature currently needs keyring access.

Start with the linked com.github.marktext.marktext.json manifest around line 18 and inventory the filesystem, temporary-directory, Secret Service, and keyring permissions. Then inspect the desktop source's keytar import and the current data center schema to identify user-facing dependencies. Done means the required permissions and their supporting features are clearly established, with unnecessary default access removed or justified.

Written by the indexing model from the issue text.