Media Picker: Implement paging

[landlogicit]

Summary

This PR improves the Media Picker performance when browsing folders
containing a large number of media items.

Changes

• Replaces entityResource.getChildren with entityResource.getPagedChildren
  in MediaPickerController.
• Adds support for orderBy/orderDirection and sets a default pageSize of 200.
• Resets pagination when entering folders and when clearing search filters.
• Updates changePagination to handle both folder browsing and search results.

Why

Currently the Media Picker loads all children of a folder in one call,
which can be very slow or even cause timeouts when the folder contains
hundreds or thousands of media items.
By using getPagedChildren we only load one page of results at a time,
improving performance and memory usage.

Breaking changes

None.
This is a pure client-side change; no modifications to EntityController
or server-side APIs are required. Existing external consumers of the
back-office API remain unaffected.

Testing

1. Open the Media Picker and navigate to a folder with a large number of media items.
2. Verify that only the configured page size (default 200) is loaded initially.
3. Use the pagination controls to navigate to other pages and confirm
   that items are loaded and displayed correctly.
4. Search for media and navigate pages to ensure search pagination still works.

[github-actions]

Hi there @landlogicit, thank you for this contribution! 👍

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[landlogicit]

Please review this pr, Thanks

[AndyButland]

Thanks very much for this @landlogicit. I've done some testing having artificially set a low number for the page size, and it all looks to work as expected.

I left a few inline comments below if you wouldn't mind taking a look at please? Some questions as to why certain changes were necessary, and some on the various comments added that feel more like points for the code reviewer and won't be useful or could be confusing once the PR is merged.

[landlogicit]

Pushed an update that:

Removes the pickPositive/pickNonNegative helpers and assigns pagination values directly, since the API guarantees valid numbers.

Cleans up or removes review-only comments.

Clarifies the purpose of resetting vm.searchOptions.filter when navigating folders.

Fixes minor indentation/formatting.

This should address all review comments and keep the MediaPickerController cleaner and easier to maintain.

[AndyButland]

Thanks for the updates. The code all looks good now, but I found an issue in testing. Do you think you might be able to find a solution to this please?

• Open media picker
• Navigate into a folder that has more items than the page size.
• Navigate to page 2.
• Close the media picker.
• Open the media picker again. You will be returned to the last folder you were looking at, however now all items are shown rather than just a single page, and there's no paging details displayed.

[landlogicit]

Thanks for the catch! I’ve updated the navigation flow so that run(), ensureWithinStartNode(), gotoStartNode() and gotoFolder() consistently return and chain the same promise, ensuring the paged fetch (getChildren → getPagedChildren) always runs when restoring the last folder.

This fixes the issue where reopening the media picker shows all items without paging metadata.

[AndyButland]

Does seem to work now, but the last commit contains quite a bit more change than I'd have expected. Can I ask if you are getting some AI help here? Not against that, but I'd like to make sure you are clear why the changes you are proposing resolve the issue, and to include only changes that are necessary. I get nervous otherwise! Could you share your method here please?

[landlogicit]

Thanks Andy, I completely understand your concern and I appreciate the careful review.
I did use AI as a support tool to speed up some repetitive editing (mainly to draft code and formatting), but every change was reviewed, tested and understood by me.

The essential fix is about promise chaining: run(), ensureWithinStartNode(), gotoStartNode(), and gotoFolder() now consistently return and chain the same promise so that the paged fetch (getChildren → getPagedChildren) always runs when restoring the last folder.
This is the key to solving the issue where reopening the picker showed all items without paging metadata.

I can certainly trim or squash the commit to show only those minimal, necessary changes if that helps make the diff clearer and keeps history clean.
Please rest assured I fully understand and stand by the solution.

[AndyButland]

Fantastic, thanks very much for the explanation @landlogicit. Don't worry about the git history, that's not a concern as we'll squash the PR when merging anyway. Now you've explained the solution you've come up with that's good for me.

[AndyButland]

Have manually tested fix by temporarily configuring a low page size, and verifying top level and lower level folders correctly handle paging.

Thanks very much for the effort on this @landlogicit, and the fix, it's much appreciated.