feat: donation banner, About tab, settings UI improvements

- Dismissible donation/open-source banner after 3+ sessions (30-day snooze)
- New About tab in Settings: version, repo link, license info
- Centralize project URLs (REPO_URL, DONATE_URL) in __init__.py, served via /health
- Center settings tab bar, reduce tab padding for 6-tab fit
- External URL save button: icon button instead of full-width text button
- Remove redundant settings footer close button
- Footer "Source Code" link replaced with "About" opening settings
- i18n keys for en/ru/zh

server/src/wled_controller/templates/index.html

@@ -105,6 +105,7 @@
             </div>
         </header>
         <div id="update-banner" class="update-banner" style="display:none"></div>
+        <div id="donation-banner" class="donation-banner" style="display:none"></div>
     <div class="container">
         <div class="tabs">
             <div class="tab-panel" id="tab-dashboard" role="tabpanel" aria-labelledby="tab-btn-dashboard">
@@ -170,7 +171,7 @@
                 <p>
                     Created by <strong>Alexei Dolgolyov</strong>
                     • <a href="mailto:dolgolyov.alexei@gmail.com">dolgolyov.alexei@gmail.com</a>
-                    • <a href="https://git.dolgolyov-family.by/alexei.dolgolyov/wled-screen-controller-mixed" target="_blank" rel="noopener">Source Code</a>
+                    • <a href="#" onclick="openSettingsModal();switchSettingsTab('about');return false" data-i18n="donation.about_title">About</a>
                 </p>
             </div>
         </footer>

server/src/wled_controller/templates/modals/settings.html

@@ -13,6 +13,7 @@
             <button class="settings-tab-btn" data-settings-tab="mqtt" onclick="switchSettingsTab('mqtt')" data-i18n="settings.tab.mqtt">MQTT</button>
             <button class="settings-tab-btn" data-settings-tab="appearance" onclick="switchSettingsTab('appearance')" data-i18n="settings.tab.appearance">Appearance</button>
             <button class="settings-tab-btn" data-settings-tab="updates" onclick="switchSettingsTab('updates')" data-i18n="settings.tab.updates">Updates</button>
+            <button class="settings-tab-btn" data-settings-tab="about" onclick="switchSettingsTab('about')" data-i18n="settings.tab.about">About</button>
         </div>
 
         <div class="modal-body">
@@ -37,7 +38,7 @@
                     <small class="input-hint" style="display:none" data-i18n="settings.external_url.hint">If set, this base URL is used in webhook URLs and other user-visible links instead of the auto-detected local IP. Example: https://myserver.example.com:8080</small>
                     <div style="display:flex;gap:0.5rem;">
                         <input type="text" id="settings-external-url" placeholder="https://myserver.example.com:8080" style="flex:1" data-i18n-placeholder="settings.external_url.placeholder">
-                        <button class="btn btn-primary" onclick="saveExternalUrl()" data-i18n="settings.external_url.save">Save</button>
+                        <button class="btn btn-icon btn-primary" onclick="saveExternalUrl()" title="Save" data-i18n-title="settings.external_url.save"><svg class="icon" viewBox="0 0 24 24"><path d="M20 6 9 17l-5-5"/></svg></button>
                     </div>
                 </div>
 
@@ -282,11 +283,13 @@
                 </div>
             </div>
 
+            <!-- ═══ About tab ═══ -->
+            <div id="settings-panel-about" class="settings-panel">
+                <div id="about-panel-content"></div>
+            </div>
+
             <div id="settings-error" class="error-message" style="display:none;"></div>
         </div>
-        <div class="modal-footer">
-            <button class="btn btn-icon btn-secondary" onclick="closeSettingsModal()" title="Close" data-i18n-title="settings.button.close" data-i18n-aria-label="aria.close">&#x2715;</button>
-        </div>
     </div>
 </div>