fixes#69Fixes `Downloader` to remove the `DownloadTask` when it is done via a completion. This will allow changing Coder deployments, which use different URLs but whose files are downloaded to the same place.

Respects the cancelation token provided to `StartDownloadAsync` even when there is another download already in progress to the same destination.

relates to#52Adds support for Coder Desktop to handle the `coder:/` URI scheme by registering for this scheme and forwarding activations to the single instance of Coder Desktop.Also removes the `Package.appxmanifest`. It is unused since Coder Desktop is not a packaged app.

https://github.com/user-attachments/assets/96d57799-0db8-4146-a93c-c157645cb4e9

Fixescoder/internal#598There is a possible race where if the cancellation token is expired, `Download()` never gets called and the tempFile is never disposed of (at least until GC). We also switch to synchronous IO so that a pending overlapped write won't block the deletion.These issues can cause races in our tests when we try to clean up the directory.

Adds logging to the Coder Desktop application.

Adds a new remote directory picker window used when creating a file syncto select the remote directory.https://github.com/user-attachments/assets/3c661969-4ba8-46b0-8e3c-e97809c2ae1d## TODOs:- [x] Use a dropdown for picking workspace agent in the file sync UI,currently it's typed out (and will crash if empty lol)- [x] Fix reactivation of the window, try to make it function like anyother system dialog windowCloses#27

Adds some logging to the mutagen controller.