fix: use showSaveFilePicker for state export with browser fallback

[patrickoleary]

Improve state file export to use the native save-as dialog when available in the browser.

Note: This fix does not allow for the user to enter a path instead of just a filename. browser technology has file system access restrictions. We still ask for just a filename here. So, there are are three cases:

• Tauri - Enter a filename and description, then Tauri presents a dialog is presented for selecting the save location.
• Modern Browser (Chrome/Edge with HTTPS or localhost) - Enter a filename and description, then 'showSaveFilePicker' presents a dialog is presented for selecting the save location.
• Browser (Not Modern [Firefox/Safari] or remote HTTP) - Enter a filename and description, then the browser saves to ~/Downloads only.

What we changed:

• Rename "Download" to "Save" throughout the state export UI (dialog title, button, menu item)
• showSaveFilePicker API (Chrome/Edge on secure contexts) — users get a native save-as dialog to choose location
• Fallback to utils.download for Firefox/Safari or non-secure contexts — saves to ~/Downloads
• Filename hint added: "Name only — save location is chosen via dialog or defaults to ~/Downloads"
• Menu item simplified: always says "Save state file" (no longer conditional on Tauri)

Fallback chain:

• Tauri → native OS save dialog (unchanged)
• Browser (Chrome/Edge, localhost/HTTPS) → showSaveFilePicker
• Browser (Firefox/Safari or remote HTTP) → utils.download to ~/Downloads

Remote host access:
The showSaveFilePicker API requires a secure context. When accessing QuickView remotely over plain http://, the native save dialog will not be available and the fallback browser download is used instead. To enable the full save-as experience for remote users:

• SSH tunnel — ssh -L 8080:localhost:8080 remote-host — browser sees localhost, secure context satisfied
• CapRover — auto-provisions HTTPS/WSS trame cloud docs

closes #78

[jourdain]

While valid I would rather capture that JS code inside here and make the click just click="utils.quickview.exportDownload(download_name)"

[jourdain]

In JS, you have access to trame but to change state variable, you will need to do window.trame.state.set("show_export_dialog", false).

[jourdain]

And the utils are available under window.trame.utils.

[jourdain]

I'll do a small cleanup in another push

[jourdain]

Done it here