feat(panel): donor strip + Telegram sponsor in footer

Public GET /api/panel/footer with env-backed URLs (defaults: Boosty + t.me sponsor). install.sh forwards PANEL_FOOTER_*. Promo only in admin SPA, not nginx landing.

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

public/styles.css

@@ -43,6 +43,64 @@ body.page {
   flex-direction: column;
 }
 
+.panel-promo-strip {
+  flex-shrink: 0;
+  position: sticky;
+  top: 0;
+  z-index: 40;
+  border-bottom: 1px solid rgba(180, 83, 9, 0.28);
+  background: linear-gradient(90deg, rgba(254, 243, 199, 0.95), rgba(255, 237, 213, 0.97));
+  backdrop-filter: blur(6px);
+}
+
+.panel-promo-strip-inner {
+  box-sizing: border-box;
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  gap: 0.5rem 1.25rem;
+  max-width: min(1120px, 100%);
+  margin: 0 auto;
+  padding: 0.5rem clamp(1rem, 3vw, 1.5rem);
+}
+
+.panel-promo-subtitle {
+  margin: 0;
+  flex: 1 1 16rem;
+  font-size: 0.84rem;
+  line-height: 1.5;
+  color: var(--text);
+}
+
+.panel-promo-links {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  gap: 0.35rem 0.65rem;
+}
+
+.panel-promo-a {
+  font-weight: 650;
+  font-size: 0.88rem;
+  color: #9a3412;
+  text-decoration: none;
+  white-space: nowrap;
+}
+
+.panel-promo-a:hover {
+  text-decoration: underline;
+}
+
+.panel-promo-sep {
+  color: var(--muted);
+  font-weight: 700;
+  user-select: none;
+}
+
+.support-line .support-promo-link {
+  white-space: nowrap;
+}
+
 .shell {
   flex: 1 0 auto;
   max-width: min(1120px, 100%);