Feature: Add chat tab font size option

[JuJuFX-dev]

Chat Tab Font Size Option

Summary

Adds a new option letting users adjust the font size of the chat tab labels (e.g. "General", "Trade", ...) independently from the actual chat text size.

Changes

EllesmereUIChat.lua

• UpdateTabStyle(): tab font size is now read from Cfg("tabFontSize") instead of being hardcoded to 11 (the DB default was already 10, but was never actually used anywhere).
• New function ECHAT.ApplyTabFontSize(): updates the font size on all currently skinned tabs live, no reload required.

EUI_Chat_Options.lua

• New "Tab Font Size" slider (range 8–20) in the cog popup next to the "Font" dropdown (alongside "Outline Mode").
• RefreshAll() now also calls ApplyTabFontSize(), so the size is correctly re-applied on e.g. profile switch.

Behavior

• Change applies instantly, no /reload needed.
• Only affects the tab label text, not the chat message text size (which is still controlled via Blizzard's right-click "Font Size" menu).