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/static/css/modal.css

@@ -352,21 +352,23 @@
 
 .settings-tab-bar {
     display: flex;
+    justify-content: center;
     gap: 0;
     border-bottom: 2px solid var(--border-color);
-    padding: 0 1.25rem;
+    padding: 0 0.75rem;
 }
 
 .settings-tab-btn {
     background: none;
     border: none;
-    padding: 8px 16px;
-    font-size: 0.9rem;
+    padding: 8px 12px;
+    font-size: 0.85rem;
     font-weight: 500;
     color: var(--text-secondary);
     cursor: pointer;
     border-bottom: 2px solid transparent;
     margin-bottom: -2px;
+    white-space: nowrap;
     transition: color 0.2s ease, border-color 0.25s ease;
 }
 
@@ -388,6 +390,102 @@
     animation: tabFadeIn 0.25s ease-out;
 }
 
+/* ── About panel ──────────────────────────────────────────── */
+.about-section {
+    text-align: center;
+    padding: 8px 0 4px;
+}
+
+.about-logo {
+    margin-bottom: 8px;
+}
+
+.about-logo .icon {
+    width: 36px;
+    height: 36px;
+    color: var(--primary-color);
+}
+
+.about-title {
+    margin: 0 0 2px;
+    font-size: 1.1rem;
+    color: var(--text-color);
+}
+
+.about-version {
+    display: inline-block;
+    margin-bottom: 8px;
+    padding: 2px 10px;
+    border-radius: 10px;
+    background: var(--bg-tertiary);
+    color: var(--text-secondary);
+    font-size: 0.8rem;
+    font-family: var(--font-mono, monospace);
+}
+
+.about-text {
+    margin: 0 0 12px;
+    color: var(--text-secondary);
+    font-size: 0.85rem;
+    line-height: 1.4;
+}
+
+.about-license {
+    margin: 10px 0 0;
+    color: var(--text-secondary);
+    font-size: 0.8rem;
+    opacity: 0.7;
+}
+
+.about-links {
+    display: flex;
+    flex-direction: column;
+    gap: 8px;
+    max-width: 280px;
+    margin: 0 auto;
+}
+
+.about-link {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+    padding: 10px 14px;
+    border-radius: var(--radius);
+    background: var(--bg-secondary);
+    border: 1px solid var(--border-color);
+    color: var(--text-color);
+    text-decoration: none;
+    font-size: 0.9rem;
+    transition: border-color 0.15s, background 0.15s;
+}
+
+.about-link:hover {
+    border-color: var(--primary-color);
+    background: var(--bg-tertiary);
+}
+
+.about-link .icon {
+    width: 18px;
+    height: 18px;
+    flex-shrink: 0;
+}
+
+.about-link .icon:last-child {
+    width: 14px;
+    height: 14px;
+    margin-left: auto;
+    color: var(--text-secondary);
+}
+
+.about-link span {
+    flex: 1;
+    text-align: left;
+}
+
+.about-link-donate .icon:first-child {
+    color: #e25555;
+}
+
 /* ── Log viewer overlay (full-screen) ──────────────────────── */
 
 .log-overlay {