Chat context indicator is not centered in its container

### Type of issue

Bug

### Description

The context indicator at the lower-right of the Chat input is horizontally offset within its rounded-square container. The indicator appears shifted to the left instead of centered. A contrasting container background makes the misalignment especially visible.

### Expected behavior

The circular context indicator is visually centered both horizontally and vertically within its container.

### Actual behavior

The circular indicator is visibly left of center.

_Created from a [Slack conversation](https://vscodeteam.slack.com/archives/C09MVCZKLP4/p1788001785987479?thread_ts=1788001785.987479&cid=C09MVCZKLP4)._