fix(updater): show header action only when update is available

Hide the header update action until a newer release is confirmed.
Register update notifications before renderer initialization so startup cannot miss them.
Refresh the public product screenshot and release metadata for v2.0.7.

renderer/app.js

@@ -369,10 +369,6 @@ async function init() {
     if (versionLabel) versionLabel.textContent = `v${version}`;
   } catch {}
 
-  // Update listeners
-  window.api.onUpdateAvailable(showUpdateBanner);
-  window.api.onUpdateProgress(handleUpdateProgress);
-
   window.api.onUploadProgress((data) => {
     handleProgress(data);
   });
@@ -660,6 +656,7 @@ function _syncHeaderUpdateState() {
       ? `Update v${version || 'unbekannt'} verfügbar. Klicken zum Installieren.`
       : 'Nach Aktualisierungen suchen';
   if (button) {
+    button.hidden = !available;
     button.classList.toggle('update-available', available);
     button.classList.toggle('is-checking', _updateCheckBusy);
     button.disabled = _updateCheckBusy;
@@ -6734,6 +6731,8 @@ function updateStatsPanel() {
 }
 
 // --- Start ---
+window.api.onUpdateAvailable(showUpdateBanner);
+window.api.onUpdateProgress(handleUpdateProgress);
 window.api.onPrepareClose(prepareForWindowClose);
 init().then(() => {
   window.api.signalCloseHandshakeReady();

renderer/index.html

@@ -53,7 +53,7 @@
     </div>
     <div class="header-spacer" aria-hidden="true"></div>
     <div class="header-cluster header-utilities">
-      <button class="header-update-button" id="headerUpdateBtn" title="Nach Aktualisierungen suchen" aria-label="Nach Aktualisierungen suchen" data-tooltip="Nach Aktualisierungen suchen">
+      <button class="header-update-button" id="headerUpdateBtn" title="Nach Aktualisierungen suchen" aria-label="Nach Aktualisierungen suchen" data-tooltip="Nach Aktualisierungen suchen" hidden>
         <svg class="header-action-icon" aria-hidden="true"><use href="#icon-download"></use></svg>
         <span class="header-update-label">Update</span>
       </button>

renderer/styles.css

@@ -1772,6 +1772,10 @@ select.hs-input { max-width: none; width: auto; min-width: 140px; }
   transition: background-color .14s, transform .14s;
 }
 
+.header-update-button[hidden] {
+  display: none;
+}
+
 .header-update-button::after {
   content: attr(data-tooltip);
   position: absolute;