[GH] (texera/gh-readonly-queue/main/pr-8771-ed0ff0aaf8b04f6cf251cba1692af57108932c82): Workflow run "Required Checks" failed!

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The GitHub Actions job "Required Checks" on texera.git/gh-readonly-queue/main/pr-8771-ed0ff0aaf8b04f6cf251cba1692af57108932c82 has failed.
Run started by GitHub user Xiao-zhen-Liu (triggered by Xiao-zhen-Liu).

Head commit for run:
acf5602f121777e58bcdcac5093a1547fe0c546f / Suryaa Charan <12...@users.noreply.github.com>
feat(frontend): explain the Kill button and where to find results and errors (#8771)

### What changes were proposed in this PR?

Two small hints in the workspace:

- **Kill button tooltip:** "Stop this run. A stopped run can't be
resumed." It was an icon-only button with no explanation.
- **Empty Result panel:** the heading now says why it is empty: "No
operator is selected." or "This operator has no results yet." With
nothing selected it also says "Click an operator to see its results. If
a run fails, its errors show here." It always adds "Errors an operator
hits while running show in that operator's Console." A failed run's
errors only appear in the Static Error tab when nothing is selected, and
errors during a run pause it and go to the operator's Console. Neither
hint shows while previewing a workflow version.

Before and after, with nothing selected (top) and an operator selected
(middle). The bottom row (a failed UDF showing its Static Error tab when
clicked) is no longer part of this PR: on main that error still arrives
as "unknown operator", because `ControlError` drops the worker that
#8668 attaches. That will be fixed in the backend in a separate PR.


<img width="1648" height="854" alt="texera-8771-before-after-v2"
src="https://github.com/user-attachments/assets/b1034c28-ce7d-4baf-b2f2-cfd935bc503e"
/>


The tooltip is a native `title`, which browsers don't draw in
screenshots. I checked it in the running app: hovering the red button
shows "Stop this run. A stopped run can't be resumed."

### Any related issues, documentation, discussions?

Part of #8736. Split out of #8737.

### How was this PR tested?

New specs in `result-panel.component.spec.ts` (nothing selected, an
operator selected, version preview) and `menu.component.spec.ts` (the
tooltip).

```
cd frontend
yarn test --include src/app/workspace/component/result-panel/result-panel.component.spec.ts --include src/app/workspace/component/menu/menu.component.spec.ts
yarn test
yarn format:ci
```

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

Generated-by: Claude Code (Claude Opus 5.5)

---------

Co-authored-by: suryaacharan <su...@suryaacharans-MacBook-Pro.local>
Co-authored-by: Claude Opus 5.5 <no...@anthropic.com>

Report URL: https://github.com/apache/texera/actions/runs/39713826386

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