feat: integrate Pi backend and Pi Web

pi-web/lib/initial-navigation.ts

@@ -0,0 +1,13 @@
+export interface InitialNavigation {
+  requestedCwd: string | null;
+  sessionId: string | null;
+}
+
+export function getInitialNavigation(searchParams: Pick<URLSearchParams, "get">): InitialNavigation {
+  const requestedCwd = searchParams.get("cwd")?.trim() || null;
+
+  return {
+    requestedCwd,
+    sessionId: requestedCwd ? null : searchParams.get("session"),
+  };
+}