feat(hub): add Downloads and Documentation landing pages

Wire hub-downloads.js for stable OTA APK resolution, expand nav i18n, and add
Session Studio download slot for alpha hub FR.

Co-authored-by: Cursor <cursoragent@cursor.com>

assets/hub-downloads.js

@@ -0,0 +1,67 @@
+(function () {
+  'use strict';
+
+  function setStatus(msg) {
+    var el = document.getElementById('hub-download-apk-status');
+    if (el) {
+      el.textContent = msg;
+    }
+  }
+
+  function resolveStableApkUrl() {
+    return fetch('/v0/ota/channel/stable.json', { cache: 'no-store' })
+      .then(function (r) {
+        if (!r.ok) {
+          throw new Error('stable channel HTTP ' + r.status);
+        }
+        return r.json();
+      })
+      .then(function (channel) {
+        var manifestUrl = channel && channel.manifestUrl;
+        if (!manifestUrl) {
+          throw new Error('stable.json missing manifestUrl');
+        }
+        return fetch(manifestUrl, { cache: 'no-store' }).then(function (r) {
+          if (!r.ok) {
+            throw new Error('manifest HTTP ' + r.status);
+          }
+          return r.json();
+        });
+      })
+      .then(function (manifest) {
+        var url = manifest && (manifest.apkUrl || manifest.bundleUrl);
+        if (!url) {
+          throw new Error('manifest missing apkUrl');
+        }
+        return url;
+      });
+  }
+
+  function wireApkButton() {
+    var btn = document.getElementById('hub-download-apk');
+    if (!btn) {
+      return;
+    }
+    btn.addEventListener('click', function () {
+      btn.disabled = true;
+      setStatus('Resolving stable OTA channel…');
+      resolveStableApkUrl()
+        .then(function (url) {
+          setStatus('Downloading…');
+          window.location.href = url;
+        })
+        .catch(function (err) {
+          setStatus('APK unavailable — run builder OTA publish (stable). ' + (err.message || err));
+        })
+        .finally(function () {
+          btn.disabled = false;
+        });
+    });
+  }
+
+  if (document.readyState === 'loading') {
+    document.addEventListener('DOMContentLoaded', wireApkButton);
+  } else {
+    wireApkButton();
+  }
+})();