feat: add tunnel status indicator with control panel in header

Green pulsing dot in the desktop header shows when Cloudflare tunnel is active.
Clicking opens a dropdown panel with tunnel URL, remote client count, auth
sessions, and start/stop/QR/revoke controls. Detects tunnel clients via
Cf-Connecting-Ip header to exclude local connections from the count.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/mocks/mock-route-context.ts

@@ -38,6 +38,7 @@ export function createMockRouteContext(options?: { sessionId?: string }) {
     batchTerminalData: vi.fn(),
     broadcastSessionStateDebounced: vi.fn(),
     batchTaskUpdate: vi.fn(),
+    getSseClientCount: vi.fn(() => 0),
 
     // -- RespawnPort --
     respawnControllers: new Map(),