fix(frontend, v1.3): list a version's files when the Versions & Files tab opens - #8884

…pens (#8838)

### What changes were proposed in this PR?

The version file tree uses virtual scroll, which measures its viewport
once and then only on scroll. On the dataset and model detail pages the
tree sits in the "Versions & Files" tab, which is hidden when the page
loads. So the files arrived while the tree measured a 0px viewport, and
it drew no rows until switching versions changed its height and forced a
re-measure.

The tree now re-measures itself whenever its container is shown or
resized, using a `ResizeObserver`. The fix is inside the tree component,
so the dataset page, the model page and the two version pickers that
reuse it are all covered. No change to the host pages.

- `user-dataset-version-filetree.component.ts`: observe the container
and call `tree.sizeChanged()` (past the library's throttle) on resize;
disconnect on destroy. The existing re-measure on a height change goes
through the same helper.
- `user-dataset-version-filetree.component.html`: `#container` ref on
the tree's container.

Before: dataset and model right after opening the tab:

<img width="1440" height="900" alt="annotated-before-dataset"
src="https://github.com/user-attachments/assets/01d99d8c-179b-455f-ab03-68357b3164f3"
/>

<img width="1440" height="900" alt="annotated-before-model"
src="https://github.com/user-attachments/assets/01631a0b-0d66-428a-8161-17ba0568efe3"
/>

After: the same pages right after opening the tab:

<img width="1440" height="900" alt="annotated-after-dataset"
src="https://github.com/user-attachments/assets/7c754657-b172-4b9f-a6a4-5c7fa53e54f7"
/>

<img width="1440" height="900" alt="annotated-after-model"
src="https://github.com/user-attachments/assets/747b0135-923d-4735-b0d8-62c2fed0b348"
/>

### Any related issues, documentation, discussions?

Closes #8833

### How was this PR tested?

One case added to
`user-dataset-version-filetree.component.browser.spec.ts`: a tree filled
while hidden renders its rows once shown. It fails without the fix (0
rows) and passes with it.

```
cd frontend
yarn ng run gui:test-browser --include='**/user-dataset-version-filetree.component.browser.spec.ts'
# Tests  6 passed (6)
yarn ng test --watch=false --include='**/user-dataset-version-filetree.component.spec.ts' --include='**/dataset-detail.component.spec.ts' --include='**/model-detail.component.spec.ts'
# Tests  249 passed (249)
```

Also checked against a local stack: on a dataset and a model with two
versions, the latest version's files are listed as soon as the "Versions
& Files" tab opens, and switching versions still updates the list.

### Was this PR authored or co-authored using generative AI tooling?

Generated-by: Claude Code (Claude Opus 5.5)

(backported from commit 9a427cc)

Co-authored-by: Meng Wang <mengw15@uci.edu>