Remove the unused UserWorkflowListItemComponent and HighlightSearchTermsPipe

### Task Summary

`UserWorkflowListItemComponent` is declared in `AppModule` but its selector `texera-user-workflow-list-item` appears in no template, so it is never rendered. `HighlightSearchTermsPipe` dies with it: the component's own template is the pipe's last remaining consumer.

### History

| | |
| --- | --- |
| **Introduced by** | #1937 (2023-05-30) — "Refactored each workflow list item into its own component" |
| **Usage removed by** | #2793 (2024-08-20) — "Generalize List Item" replaced it with the generic `ListItemComponent`, deleting the last two `texera-user-workflow-list-item` uses from `search-results.component.html` |

The pipe has its own thread: introduced by #2386 (2024-02-16, "Highlight search terms in search result"), it kept a second consumer until #7463 (2026-08-29, "remove the deprecated project feature") dropped `entry.name | highlightSearchTerms` from that template. Since then the only place the pipe is used is this dead component, so the two must be removed together — remove the component alone and the pipe becomes dead in the same commit.

Dead for about two years. Pure deletion, no behaviour change: −1,104 lines (component 201 + template 210 + styles 21 + its spec 559, pipe 40 + its spec 67, plus six wiring lines).

### Task Type

- [x] Refactor / Cleanup