feat(web/ui): unify session opening and add repo card in project list

- Add openSession utility with tab deduplication/focus
- Use openSession in navbar live sessions, use-instance-actions, and project tool links
- Pass onAddRepository to ProjectListItem and add dashed 'Add Repository' card
- Style add-repo card in projects.css

apps/web/src/utils/open-session.ts

@@ -0,0 +1,24 @@
+import type { Session } from "../api/sessions";
+
+const tabRefs = new Map<string, Window | null>();
+
+export function openSession(session: Session): void {
+	const key = session.id;
+	const existing = tabRefs.get(key);
+	if (existing && !existing.closed) {
+		existing.focus();
+		return;
+	}
+
+	let url: string;
+	if (session.url) {
+		url = session.url;
+	} else if (session.tool_type_interfaces?.includes("terminal")) {
+		url = `/instances/${session.id}/terminal`;
+	} else {
+		url = `/projects/${session.project_id}`;
+	}
+
+	const w = window.open(url, `session-${session.id}`);
+	tabRefs.set(key, w);
+}