feat(shell): polish header/hero overlay and footer zibll classes

Make show-slide header overlay the hero, dual-class nav/footer shells
toward zibll selectors, and add a small footer layout bridge for logo,
contact, and float buttons.

assets/css/frontend/footer/zibll-shell.css

@@ -0,0 +1,50 @@
+/**
+ * Footer zibll shell dual-class bridge
+ */
+.footer.site-footer {
+  position: relative;
+  width: 100%;
+}
+
+.footer .container-footer,
+.footer .container-fluid.container-footer {
+  width: 100%;
+  max-width: var(--container, 1200px);
+  margin-left: auto;
+  margin-right: auto;
+  padding-left: 15px;
+  padding-right: 15px;
+}
+
+.footer .footer-logo {
+  max-height: 48px;
+  width: auto;
+  display: inline-block;
+}
+
+.footer .footer-contact a {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  margin-right: 10px;
+}
+
+.footer .fcode-links a {
+  display: inline-block;
+  margin-right: 12px;
+  margin-bottom: 6px;
+}
+
+.footer .footer-conter {
+  margin: 0;
+  line-height: 1.7;
+}
+
+/* Keep float-right above content, zibll-like */
+#float-right-btns.float-right,
+.float-right {
+  position: fixed;
+  right: 16px;
+  bottom: 80px;
+  z-index: 90;
+}