fix(desktop): label the flat advanced-fields block as Advanced

The flat profile panel's advanced-fields block (active_provider etc.)
rendered directly beneath the new MCP Servers label with no header of
its own, so it visually read as part of the MCP Servers group. Add a
matching text-only 'Advanced' header so the block reads as its own
group, mirroring the label style already used for MCP Servers.

Co-authored-by: Will Pfleger <pfleger.will@gmail.com>
Signed-off-by: Will Pfleger <pfleger.will@gmail.com>

desktop/src/features/agents/ui/AgentConfigPanel.tsx

@@ -426,6 +426,9 @@ export function AgentConfigPanel({
 
       {advanced.length > 0 && advancedMode === "flat" ? (
         <div className="divide-y divide-border/50 border-t border-border/50">
+          <p className="px-4 py-3 text-xs font-medium text-foreground">
+            Advanced
+          </p>
           {advanced.map((field) => (
             <AdvancedRow
               key={field.key}

desktop/tests/e2e/config-bridge-screenshots.spec.ts

@@ -245,8 +245,10 @@ test.describe("config bridge screenshots", () => {
 
     const panel = await openAgentProfileFromChannel(page, "Goose Agent");
 
-    // Advanced runtime fields render directly in the profile panel's flat list.
+    // Advanced runtime fields render directly in the profile panel's flat list,
+    // grouped under their own "Advanced" header.
     await expect(panel.getByText("active_provider")).toBeVisible();
+    await expect(panel.getByText("Advanced", { exact: true })).toHaveCount(1);
     // MCP servers render once each under their group label.
     await expect(panel.getByText("developer", { exact: true })).toHaveCount(1);
     await expect(panel.getByText("MCP Servers", { exact: true })).toHaveCount(