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/history/page.tsx

@@ -1,7 +1,8 @@
 "use client";
 
 import { useState } from "react";
-import { Search, X } from "lucide-react";
+import Link from "next/link";
+import { Search, X, Plus } from "lucide-react";
 import { useSessions, useSessionSearch } from "@/lib/hooks";
 import { SessionCard } from "@/components/SessionCard";
 
@@ -24,7 +25,16 @@ export default function HistoryPage() {
 
   return (
     <div className="space-y-4">
-      <h1 className="text-xl font-semibold" style={{ color: "var(--text-1)" }}>History</h1>
+      <div className="flex items-center justify-between">
+        <h1 className="text-xl font-semibold" style={{ color: "var(--text-1)" }}>History</h1>
+        <Link
+          href="/history/new"
+          className="p-2 rounded-xl active:scale-95 transition-all"
+          style={{ background: "var(--accent-dim)", color: "var(--accent)" }}
+        >
+          <Plus size={18} />
+        </Link>
+      </div>
 
       <div className="relative">
         <Search size={16} className="absolute left-3 top-1/2 -translate-y-1/2" style={{ color: "var(--text-3)" }} />