docs: Add screenshots to documentation pages

[axel-krapotke]

Context

The documentation at odin.syncpoint.io/docs was generated from specs and currently lacks visual aids. Screenshots would significantly improve usability.

Missing Screenshots

Shapes (features/shapes.md)

• Shapes dropdown menu in toolbar
• Text shape with markdown formatting (showing properties panel)
• Line shape example with styled properties
• Polygon shape example with fill color

Other Pages (review needed)

• MGRS Graticule overlay examples (different zoom levels)
• Symbology placement and editing
• NIDO API usage example (optional, could be diagrams)
• Collaboration setup (Matrix integration)
• Tile services configuration
• Elevation data visualization

Guidelines

• Screenshots should be taken at a consistent window size
• Use meaningful map content (not empty maps)
• Crop to relevant UI area where possible
• Save as PNG for UI elements, JPG for full map views
• Place in docs-src/docs/<section>/img/ directories