New session creation page, + button on History

- /history/new: compose first message, creates web session, sends, redirects
- POST /api/sessions proxy route
- History page gets + button in header

app/api/sessions/route.ts

@@ -0,0 +1,21 @@
+import { NextRequest, NextResponse } from "next/server";
+
+const BACKEND = process.env.HERMES_BACKEND_URL || "http://127.0.0.1:8643";
+
+export async function POST(req: NextRequest) {
+  const body = await req.text();
+  try {
+    const res = await fetch(BACKEND + "/api/sessions", {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body,
+    });
+    const data = await res.text();
+    return new NextResponse(data, {
+      status: res.status,
+      headers: { "content-type": "application/json" },
+    });
+  } catch {
+    return NextResponse.json({ error: "backend unreachable" }, { status: 502 });
+  }
+}