Feature Request: Embed collaboration editor (OnlyOffice/Collabora) in-app instead of browser handoff

[orrinwitt]

Problem

When opening an office document (via OnlyOffice or Collabora integration) in the OpenCloud Android app, the app hands off to the system browser to load the editor. This breaks the user experience:

• User taps a document → external browser opens → editor loads there
• Auth/session context is lost between the app and browser
• No way to return to the file browser after editing without switching apps
• Feels like a broken integration rather than a seamless flow

Expected Behavior

The editor should load in-app via a WebView, maintaining the existing auth/session context — similar to how the Nextcloud Android app embeds Collabora editors seamlessly. The user taps a document, the editor opens within the app, they edit and close back to the file list without ever leaving the app.

Context

• The web UI already embeds the editor via iframe with WOPI, so the rendering layer works
• Nextcloud's Android app demonstrates this is feasible with WOPI-based editors (Collabora)
• The current browser handoff makes mobile document editing impractical for regular use
• Roadmap issue Upload fotos/videos in subfolders per year/month #46 tracks Android app improvements but doesn't mention editor embedding