fix: use badge colors for auto label to improve dark theme readability

Fixes #559

The 'auto' badge on tool rows in the Usage Analysis panel was using
--bg-secondary / --text-muted / --border-subtle which have low contrast
against dark editor backgrounds.

Replace with --badge-bg / --badge-fg (mapped to VS Code's
vscode-badge-background / vscode-badge-foreground tokens) which are
designed to have proper contrast in both light and dark themes, and
remove the border since the badge background provides sufficient visual
separation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: rajbos

vscode-extension/src/webview/usage/main.ts

@@ -260,7 +260,7 @@ function renderToolsTable(byTool: { [key: string]: number }, limit = 10, nameRes
 		const friendly = escapeHtml(nameResolver(tool));
 		const idEscaped = escapeHtml(tool);
 		const autoBadge = AUTOMATIC_TOOL_SET_WV.has(tool)
-			? `<span title="Automatic tool — Copilot uses this internally and it does not count toward fluency scoring" style="margin-left:6px; padding:1px 5px; font-size:10px; border-radius:3px; background:var(--bg-secondary); color:var(--text-muted); border:1px solid var(--border-subtle); vertical-align:middle;">auto</span>`
+			? `<span title="Automatic tool — Copilot uses this internally and it does not count toward fluency scoring" style="margin-left:6px; padding:1px 5px; font-size:10px; border-radius:3px; background:var(--badge-bg); color:var(--badge-fg); vertical-align:middle;">auto</span>`
 			: '';
 		return `
 		    <tr>