Add a per-download custom output location picker

Problem

Currently, downloads are saved to the application's configured default output directory. This works well for a fixed workflow, but becomes inconvenient when downloads need to be organized into different folders.

For example, a user may want to save videos from different projects, courses, or topics into separate folders without having to change the global download directory every time.

There is currently no convenient way to choose a different output folder directly when configuring an individual download.

Proposed solution

Add an Output Location picker to the download options panel on the main downloads page (Omnibox).

The picker should:

• Show the current default output directory.
• Allow the user to browse and select a different local folder for the current download.
• Remember previously selected folders so they can be reused for future downloads.
• Automatically select a newly browsed folder for the current download.
• Allow saved folders to be removed from the list.
• Use the selected location when starting both individual and batch downloads.
• Preserve the saved folder list across application restarts.

The global default output directory would remain unchanged. This feature would simply provide a convenient per-download override.

Alternatives considered

Changing the Global Default Directory

This would require changing the application's global setting every time a download needs to go somewhere different, which is inconvenient for users who frequently organize downloads into different folders.

Choosing the Folder After Starting the Download

This would make the workflow less straightforward and could complicate downloads that have already started processing.

Not Remembering Previously Selected Folders

This would solve the immediate problem but would require repeatedly browsing to the same directories. Persisting previously used locations makes the feature much more useful for recurring workflows.

Additional context

The proposed picker would be located alongside the existing download options, such as format and quality, so the output location can be configured before clicking Download.

The selected folder would apply to the current download without changing the application's global default directory.