style: Improve markdown editor styling and functionality

- Update dark mode button icon and styling
- Add styling for new collection button
- Apply default iframe styles in preview pane
- Adjust vertical divider height in header buttons
- Improve handling of JSX-like attributes in markdown
- Add support for new collection functionality
- Refine file loading logic in view mode
- Improve dark mode toggle icon and integration
- Update UI for edit/view mode toggle button

collections/tech/presentation.md

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+## Mycelium Product Presentation
+
+This document provides an overview of the Mycelium technology stack (as commercially sold my our company GeoMind).
+
+
+
+<div style={{
+  position: 'relative',
+  width: '100%',
+  height: 0,
+  paddingTop: '56.25%',
+  marginTop: '1.6em',
+  marginBottom: '0.9em',
+  overflow: 'hidden',
+  borderRadius: '8px',
+  willChange: 'transform'
+}}>
+  <iframe
+    src="https://www.canva.com/design/DAG0UtzICsk/rqXpn5f3ibo2OpX-yDWmPQ/view?embed"
+    style={{
+      position: 'absolute',
+      width: '100%',
+      height: '100%',
+      top: 0,
+      left: 0,
+      border: 'none',
+      padding: 0,
+      margin: 0
+    }}
+    allowFullScreen={true}
+    allow="fullscreen">
+  </iframe>
+</div>
+
+<div style={{ marginTop: '10px' }}>
+  <a href="https://www.canva.com/design/DAG0UtzICsk/rqXpn5f3ibo2OpX-yDWmPQ/view"
+     target="_blank"
+     rel="noopener"
+     style={{ textDecoration: 'none' }}>
+    Geomind Product Intro 2025 (based on mycelium technology)
+  </a>
+</div>