Replace Copy Dataset Mako with Vue Component

[guerler]

This PR replaces the legacy Mako-based copy-history-items flow with a FastAPI endpoint and a Vue3 component, preserving functionality one hundred percent. The former controller logic is moved into a single POST /api/datasets/copy endpoint backed by a Pydantic payload and response model, removing unused parameters (do_copy, target_history_id, message fields, refresh frames) and switching errors to standard API exceptions. The dataset and collection copy logic is unchanged and now resides in DatasetManager.copy_datasets, supporting multi-target copies and optional new-history creation exactly as before. The Vue component replaces the Mako form, sends JSON payloads, and reconstructs the success message client-side while maintaining the same behavior as previously.

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[mvdbeek]

It is still by far the fastest way to copy multiple datasets. Admittedly I didn't even know it was still reachable in the UI (the cog wheel options are really not that intuitive). Can we merge this after the 24.0 branch and then make sure there's some kind of replacement (maybe through the side-by-side history view) ?

[guerler]

@mvdbeek we do have a replacement for this feature now, users can select multiple files in the history and drag/drop them into another history using the multi history view interface thx to @ahmedhamidawan.

[wm75]

Not only is it still the fastest way as @mvdbeek points out, but I'm also still using this a lot in daily work.
Mostly out of old habits, but, importantly, also on touch screen devices. Last time I checked drag and drop in the multi-history view still wasn't working on mobile and it's that old alternative that saved me then.

I'm not opposed to removing the mako page, but then we need to make sure we have 100% of its functionality available elsewhere.

[jmchilton]

API looks solid to me - thanks for migrating the selenium tests and rebasing on the vitest work.