tab-complete should be supported for @ name

[Dan-Linden]

Environment

Second Life Test 7.1.13.14538693756 (64bit)

Description

tab-complete should be supported for @ name

Reproduction steps

1. Type @ and the first letter of your name (or some nearby users' name) and so that a name is highlighted.
2. Press tab

Observed: Focus moves to the Emoji button.

Expected: This should work the same way as picking a name with Enter. The highlighted name should be added to the chat line and the cursor placed after it.

[AtlasLinden]

Passed QA.
Verified on the Second Life Release 7.1.14.14742193597 (2025.04) on Win11/MacOS