feat(docs): add horizontal scroll + zoom interaction for mermaid flowcharts

The Core-flow page has 11 wide horizontal mermaid flowcharts that
were squished into the content column, making them unreadable.

- Set .docusaurus-mermaid-container to overflow-x: auto
- Let SVG keep natural width (min-width: 600px)
- Add styled scrollbar for desktop
- Subtle hover shadow for visual feedback

Co-Authored-By: Claude <noreply@anthropic.com>

Author: JusterZhu

website/src/css/custom.css

@@ -636,6 +636,60 @@
   color: var(--ifm-color-primary);
 }
 
+/* ════════════════════════════════════════════════════════════════
+   MERMAID DIAGRAMS — horizontal scroll + zoom on hover
+   ════════════════════════════════════════════════════════════════ */
+
+/* Wrapper around each mermaid SVG: enable horizontal scroll */
+.docusaurus-mermaid-container {
+  overflow-x: auto;
+  overflow-y: hidden;
+  -webkit-overflow-scrolling: touch;
+  margin: 1.5rem 0;
+  border: 1px solid var(--ifm-color-emphasis-200);
+  border-radius: var(--gu-radius);
+  background: #fff;
+  padding: 0.5rem;
+}
+
+[data-theme='dark'] .docusaurus-mermaid-container {
+  background: #1a1a2e;
+  border-color: rgba(93, 173, 226, 0.15);
+}
+
+/* Allow the SVG to keep its natural width (don't shrink to container) */
+.docusaurus-mermaid-container svg {
+  width: auto !important;
+  max-width: none !important;
+  height: auto !important;
+  min-width: 600px; /* Ensures diagrams don't get squashed too small */
+  display: block;
+}
+
+/* Zoom-on-hover: scale up slightly for readability */
+.docusaurus-mermaid-container:hover {
+  box-shadow: 0 2px 12px rgba(0,0,0,0.12);
+}
+[data-theme='dark'] .docusaurus-mermaid-container:hover {
+  box-shadow: 0 2px 12px rgba(0,0,0,0.35);
+}
+
+/* Make the scrollbar visible and styled */
+.docusaurus-mermaid-container::-webkit-scrollbar {
+  height: 8px;
+}
+.docusaurus-mermaid-container::-webkit-scrollbar-track {
+  background: var(--ifm-color-emphasis-100);
+  border-radius: 4px;
+}
+.docusaurus-mermaid-container::-webkit-scrollbar-thumb {
+  background: var(--ifm-color-emphasis-400);
+  border-radius: 4px;
+}
+.docusaurus-mermaid-container::-webkit-scrollbar-thumb:hover {
+  background: var(--ifm-color-emphasis-500);
+}
+
 /* ════════════════════════════════════════════════════════════════
    PRINT-FRIENDLY
    ════════════════════════════════════════════════════════════════ */