feat(docs): add OG image and prune unused assets

docs/app/base.css

@@ -4,27 +4,19 @@
   --brand-500: #a855f7;
   --brand-400: #c084fc;
   --brand-300: #d8b4fe;
-  --brand-200: #ead4ff;
-  --brand-100: #f5eaff;
   --ink: #171419;
   --ink-soft: #4f4854;
   --ink-muted: #786f7d;
   --paper: #fbfafc;
   --paper-warm: #f7f4f8;
   --surface: #ffffff;
-  --surface-soft: #f3eff5;
   --line: #e5dfe8;
   --line-strong: #d4cad8;
-  --dark: #17131a;
-  --dark-raised: #211a25;
   --dark-line: #362c3c;
-  --success: #24a66b;
   --warning: #f59e0b;
   --font-sans: Inter, ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
   --font-display: "Avenir Next", Avenir, "Segoe UI", ui-sans-serif, sans-serif;
   --font-mono: "SFMono-Regular", Consolas, "Liberation Mono", monospace;
-  --shadow-sm: 0 8px 30px rgba(41, 25, 48, 0.07);
-  --shadow-lg: 0 30px 90px rgba(49, 25, 60, 0.14);
   --shell: 1220px;
 }
 
@@ -163,13 +155,6 @@ p {
   height: 18px;
 }
 
-.button-small {
-  min-height: 44px;
-  padding-inline: 16px;
-  border-radius: 11px;
-  font-size: 13px;
-}
-
 .button-primary {
   background: linear-gradient(135deg, var(--brand-500), var(--brand-700));
   box-shadow: 0 12px 28px rgba(132, 47, 238, 0.24), inset 0 1px rgba(255, 255, 255, 0.35);
@@ -180,35 +165,6 @@ p {
   box-shadow: 0 16px 34px rgba(132, 47, 238, 0.3), inset 0 1px rgba(255, 255, 255, 0.35);
 }
 
-.button-ghost {
-  border-color: var(--line);
-  background: rgba(255, 255, 255, 0.72);
-  color: var(--ink);
-}
-
-.button-ghost:hover {
-  border-color: var(--line-strong);
-  background: white;
-  box-shadow: var(--shadow-sm);
-}
-
-.button-dark {
-  background: var(--ink);
-  color: white;
-}
-
-.button-light {
-  background: white;
-  color: #211925;
-  box-shadow: 0 12px 40px rgba(0, 0, 0, 0.18);
-}
-
-.button-dark-ghost {
-  border-color: rgba(255, 255, 255, 0.2);
-  background: rgba(255, 255, 255, 0.06);
-  color: white;
-}
-
 .motion-ready .reveal {
   opacity: 0;
   transform: translateY(28px);