improvement(welcome): prominent open-source callout in the page body

Add an accent-tinted 'Free and open source' band between the app preview and the feature grid
— a short line about reading the code / self-hosting / filing an issue, linking to the public
repo. The compact footer link stays. Trilingual.

frontend/src/components/Welcome.tsx

@@ -1,6 +1,7 @@
 import { useEffect, useState } from "react";
 import { useTranslation } from "react-i18next";
 import {
+  ArrowRight,
   Code2,
   Expand,
   Filter,
@@ -64,6 +65,29 @@ export default function Welcome() {
           onOpen={open}
         />
 
+        {/* Open source — Siftlode's code is public; nudge visitors to read it or self-host. The
+            footer keeps a compact link too. */}
+        <a
+          href={REPO_URL}
+          target="_blank"
+          rel="noopener noreferrer"
+          className="group mt-8 flex flex-col items-center gap-x-4 gap-y-2 rounded-2xl border border-accent/25 bg-accent/[0.06] px-5 py-4 text-center sm:flex-row sm:text-left hover:border-accent/50 transition"
+        >
+          <span className="grid place-items-center w-10 h-10 rounded-xl bg-accent/15 text-accent shrink-0">
+            <Code2 className="w-5 h-5" />
+          </span>
+          <span className="flex-1">
+            <span className="block font-semibold">{t("welcome.openSource.title")}</span>
+            <span className="block text-sm text-muted leading-relaxed">
+              {t("welcome.openSource.body")}
+            </span>
+          </span>
+          <span className="inline-flex items-center gap-1 text-sm font-medium text-accent whitespace-nowrap">
+            {t("welcome.openSource.link")}
+            <ArrowRight className="w-4 h-4 transition group-hover:translate-x-0.5" />
+          </span>
+        </a>
+
         {/* Features */}
         <section className="mt-14">
           <h2 className="text-2xl font-semibold text-center">{t("welcome.features.heading")}</h2>