docs: update website with cross-device sync feature and fix download links

Point download cards to /releases/latest, fix Chrome ZIP filename in
sideload instructions, add Cross-Device Sync to features grid.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: vveerrgg

docs/index.html

@@ -351,6 +351,10 @@ <h4>📝 Encrypted Vault</h4>
                     <h4>🔑 API Key Storage</h4>
                     <p>Encrypted API keys synced across devices</p>
                 </div>
+                <div class="feature">
+                    <h4>🔄 Cross-Device Sync</h4>
+                    <p>Profiles, vault, and settings sync via Google/iCloud</p>
+                </div>
                 <div class="feature">
                     <h4>👤 Multi-Profile</h4>
                     <p>Manage multiple Nostr identities with per-site permissions</p>
@@ -366,17 +370,17 @@ <h4>📱 Cross-Platform</h4>
             <h2>Download & Install</h2>
 
             <div class="download-grid">
-                <a href="https://github.com/HumanjavaEnterprises/nostrkey.browser.plugin.src/releases" class="download-card">
+                <a href="https://github.com/HumanjavaEnterprises/nostrkey.browser.plugin.src/releases/latest" class="download-card">
                     <svg viewBox="0 0 24 24" fill="#4285F4"><circle cx="12" cy="12" r="10"/><path fill="#fff" d="M12 6a6 6 0 100 12 6 6 0 000-12zm0 10.5a4.5 4.5 0 110-9 4.5 4.5 0 010 9z"/></svg>
                     <h4>Chrome</h4>
                     <p>Manifest V3</p>
                 </a>
-                <a href="https://github.com/HumanjavaEnterprises/nostrkey.browser.plugin.src/releases" class="download-card">
+                <a href="https://github.com/HumanjavaEnterprises/nostrkey.browser.plugin.src/releases/latest" class="download-card">
                     <svg viewBox="0 0 24 24" fill="#0066CC"><rect width="24" height="24" rx="5" fill="#0066CC"/><text x="12" y="17" text-anchor="middle" fill="white" font-size="14" font-weight="bold">S</text></svg>
                     <h4>Safari (macOS)</h4>
                     <p>Xcode build</p>
                 </a>
-                <a href="https://github.com/HumanjavaEnterprises/nostrkey.browser.plugin.src/releases" class="download-card">
+                <a href="https://github.com/HumanjavaEnterprises/nostrkey.browser.plugin.src/releases/latest" class="download-card">
                     <svg viewBox="0 0 24 24" fill="#147EFB"><rect width="24" height="24" rx="5" fill="#147EFB"/><rect x="7" y="3" width="10" height="18" rx="2" fill="white"/></svg>
                     <h4>Safari (iOS)</h4>
                     <p>Xcode build</p>
@@ -385,8 +389,8 @@ <h4>Safari (iOS)</h4>
 
             <h3>Chrome Installation (Sideload)</h3>
             <ol style="list-style: decimal; padding-left: 24px;">
-                <li style="padding-left: 8px;">Download the latest release from <a href="https://github.com/HumanjavaEnterprises/nostrkey.browser.plugin.src/releases" style="color: var(--accent);">GitHub Releases</a></li>
-                <li style="padding-left: 8px;">Unzip the <code>chrome.zip</code> file</li>
+                <li style="padding-left: 8px;">Download <code>nostrkey-chrome-v*.zip</code> from the <a href="https://github.com/HumanjavaEnterprises/nostrkey.browser.plugin.src/releases/latest" style="color: var(--accent);">latest release</a></li>
+                <li style="padding-left: 8px;">Unzip the file</li>
                 <li style="padding-left: 8px;">Open <code>chrome://extensions/</code> in Chrome</li>
                 <li style="padding-left: 8px;">Enable <strong>Developer mode</strong> (top right toggle)</li>
                 <li style="padding-left: 8px;">Click <strong>Load unpacked</strong> and select the unzipped folder</li>