fix(layout): add min-h-0 to main-content — prevents grid overflow

Root cause found via DOM inspection: main-content (a CSS grid item) had
default min-height:auto, which prevented the grid from constraining it
below its content height. Content grew to 994px in a 975px viewport,
pushing the FlowPilot action bar (Resolve/Escalate/Pause) 75px below
the visible area. overflow:hidden on the grid clipped it invisibly.

Fix: min-h-0 on main-content allows the grid to shrink it to fit,
completing the height chain all the way down to the action bar.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/layout/AppLayout.tsx

@@ -188,7 +188,7 @@ export function AppLayout() {
       )}
 
       {/* Main Content */}
-      <main className="main-content flex flex-col overflow-hidden">
+      <main className="main-content flex flex-col overflow-hidden min-h-0">
         <EmailVerificationBanner />
         <ViewTransitionOutlet />
       </main>