chat: use command center colors for compact agent control

[Elijah King (eli-w-king)]

Fixes #329092

What changed

• use commandCenter.background for the compact agent control so it matches the command center it replaces
• use commandCenter.activeForeground for the compact input area on hover
• preserve the separate agentStatusIndicator.background behavior outside compact mode

Validation

• ran pre-commit hygiene
• transpiled the workbench and compiled the Copilot extension
• verified rest and hover colors in all 19 built-in color themes, including both high-contrast themes

[Copilot]

Pull request overview

Updates the compact agent control to visually match the command center while preserving non-compact styling.

Changes:

• Uses the command center background throughout compact mode.
• Uses the active command center foreground on input hover.

Show a summary per file

File	Description
agenttitlebarstatuswidget.css	Aligns compact agent control rest and hover colors with command center tokens.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Balanced