feat(brand): emblem behind hero text + Powered By footer with logo

Address review: the SVG footer badge rendered too small, and the default
hero should feature the Runic Gateway emblem rather than the moon.

- Footer: drop powered-by.svg; render the emblem PNG beside a "Powered by
  Runic Gateway" label (left-justified, info text stays centered).
- Default hero: brand.hero (and the client fallbacks) now default to the
  emblem PNG. The untouched default hero centers the square emblem behind
  the text as a medallion with a symmetric legibility overlay (per-layer
  background-size so the overlay stays full-bleed). BRAND_HERO still
  overrides.
- Admin login / player shell / maintenance backgrounds center the emblem
  as a capped medallion instead of a cropped full-bleed cover.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XmHdsbnLzDMAVQkAoTQSBe

client/src/styles/theme.css

@@ -1020,10 +1020,29 @@ button[disabled] {
   margin: 0 auto;
 }
 .site-footer-badge {
-  height: 56px;
-  width: auto;
+  display: flex;
+  align-items: center;
+  gap: 10px;
   flex: 0 0 auto;
-  opacity: 0.85;
+}
+.site-footer-badge img {
+  height: 48px;
+  width: 48px;
+  object-fit: contain;
+  filter: drop-shadow(0 0 6px rgba(127, 153, 189, 0.35));
+}
+.site-footer-badge span {
+  font-size: 0.72rem;
+  line-height: 1.25;
+  letter-spacing: 0.06em;
+  text-transform: uppercase;
+  color: var(--dim);
+  text-align: left;
+}
+.site-footer-badge strong {
+  color: var(--muted);
+  font-weight: 700;
+  letter-spacing: 0.04em;
 }
 .site-footer-info {
   display: flex;
@@ -1045,8 +1064,9 @@ button[disabled] {
   .site-footer-inner {
     flex-direction: column;
   }
-  .site-footer-badge {
-    height: 44px;
+  .site-footer-badge img {
+    height: 40px;
+    width: 40px;
   }
 }