feat: open all sessions in new tabs; sidebar terminal links

Sidebar SessionItem was only opening web tool URLs in new tabs.
Terminal sessions linked to the project page in the same tab.
SessionCard 'Open' buttons for terminal sessions navigated in-place.

Changes:
- app-shell.tsx: SessionItem now builds terminal URLs
  (/instances/:id/terminal) and always uses target=_blank
- session-card.tsx: compute openHref for both web and terminal sessions,
  render <a> links with target=_blank instead of callback buttons
- use-instance-actions.ts: handleOpen now uses window.open(..., '_blank')
  for terminal sessions and project fallback

All session opening (sidebar, cards, callbacks) now consistently opens
in a new tab.

Quality gates: tsc clean

apps/web/src/components/app-shell.tsx

@@ -35,11 +35,23 @@ const NAV_ITEMS: {
 const SessionItem = ({ session }: { session: Session }) => {
 	const isRunning = session.status === "running";
 
+	// Determine the link target:
+	// - Web tools open their tunnel URL
+	// - Terminal tools open the terminal page
+	// - Everything else falls back to the project page
+	const hasTerminal = session.tool_type_interfaces.includes("terminal");
+	const hasWeb = session.tool_type_interfaces.includes("web");
+	const href = session.url && hasWeb
+		? session.url
+		: hasTerminal
+			? `/instances/${session.id}/terminal`
+			: `/projects/${session.project_id}`;
+
 	return (
 		<a
-			href={session.url ?? `/projects/${session.project_id}`}
-			target={session.url ? "_blank" : undefined}
-			rel={session.url ? "noopener noreferrer" : undefined}
+			href={href}
+			target="_blank"
+			rel="noopener noreferrer"
 			className="nav-item session-item"
 			title={`${session.display_name} (${session.status})`}
 		>