feat: add map-editor plugin with interactive OSM map and markers

Implement Phase 1 of custom Kirby plugin for editing interactive maps:
- OpenStreetMap base layer with MapLibre GL JS
- Click to add markers, drag to reposition
- Marker list sidebar with selection and deletion
- Auto-save with debounce (YAML format)
- Add marker button creates marker at current map center
- Max 50 markers per map (configurable)
- Clean UI with marker counter

Blueprint updated to use new map-editor field type instead of placeholder.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

public/site/plugins/map-editor/README.md

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+# Map Editor Plugin for Kirby CMS
+
+Interactive map editor plugin for Kirby CMS using MapLibre GL JS. Create print-ready maps with draggable markers and rich content.
+
+## Phase 1 - Complete ✓
+
+Basic map functionality with OSM tiles and draggable markers.
+
+### Features
+
+- Interactive OpenStreetMap base layer
+- Add markers by clicking on the map
+- Drag & drop markers to reposition
+- Delete markers with confirmation
+- Marker list sidebar
+- Real-time YAML data storage
+- Zoom controls
+- Maximum 50 markers per map (configurable)
+
+### Installation
+
+1. Plugin is located in `/public/site/plugins/map-editor/`
+2. Dependencies are already installed via `npm install`
+3. Plugin is built and ready to use
+
+### Usage in Blueprints
+
+```yaml
+mapdata:
+  label: Carte
+  type: map-editor
+  defaultCenter: [43.836699, 4.360054]  # [latitude, longitude]
+  defaultZoom: 13
+  maxMarkers: 50
+```
+
+### Data Format
+
+The plugin stores data in YAML format in the page content file:
+
+```yaml
+Mapdata:
+  background:
+    type: osm
+  center:
+    lat: 43.836699
+    lon: 4.360054
+  zoom: 13
+  markers:
+    - id: marker_1234567890_abc
+      position:
+        lat: 43.836699
+        lon: 4.360054
+      icon:
+        type: default
+      title: ""
+      content: []
+```
+
+### Development
+
+Build the plugin during development:
+
+```bash
+cd /public/site/plugins/map-editor
+npm run dev    # Watch mode
+npm run build  # Production build
+```
+
+### Next Phases (Planned)
+
+- **Phase 2**: Rich marker content (titles, custom icons, text + images)
+- **Phase 3**: Geocoding search with Nominatim API
+- **Phase 4**: Static map rendering for PDF export
+
+## Technical Details
+
+- **MapLibre GL JS**: Open-source map rendering engine
+- **OSM Tiles**: Free OpenStreetMap tiles
+- **Kirbyup**: Build tool for Kirby panel plugins
+- **Vue 2**: Kirby panel uses Vue 2 (not Vue 3)
+
+## Browser Support
+
+- Modern browsers with ES6+ support
+- WebGL required for MapLibre