Task output files: platform affordance for save-to-Files / open-with

<!-- Template: nextcloud/server .github/ISSUE_TEMPLATE/Feature_request.md. --> Task output files: platform affordance for save-to-Files / open-with > [!TIP] > Help move this idea forward > * Use the 👍 reaction to show support for this feature. > * Avoid commenting unless you have relevant information to add; unnecessary comments create noise for subscribers. > * Subscribe to receive notifications about status changes and new comments. --- <!-- DO NOT EDIT ABOVE THIS LINE --> Is your feature request related to a problem? Please describe. Task outputs live in appdata and are reachable only through task-scoped download routes. There is no platform-level way to save an output into the user files or hand it to an open-with handler, which every consuming app currently re-invents. The assistant open-in-office flow depends on the same seam, and the FileDisplay name bug is the rendering half of this gap. Describe the solution you'd like A supported flow (core…