MapControl floating map toolbar plugin

[CarsonDavis]

Description

Second half of the split of #115 (by @BhattaraiSijan) — the MapControl plugin itself, stacked on #237, which provides the core APIs it consumes. All 27 files are byte-identical to the original branch; commits are attributed to the original author. Do not merge before #237.

Closes #98.

Adds MapControl, a floating toolbar over the map with four features, each enabled/disabled per-mission from the Configure page. The plugin is bus-only: the React component is MMGIS-independent and a thin wrapper translates its callbacks into mmgisAPI calls (all provided by #237).

Geocode search

On each keystroke we hit the Nominatim API with the URL-encoded query — debounced 300ms, only firing for queries ≥2 chars, limit=5. No API key or backend (public endpoint). On selecting a result we reorder Nominatim's bbox into Leaflet order, fly to it via map:fitBounds, and drop a pin via map:createLayer.

Basemap switching

Lists the styles from msv.basemap.styles[] (or provider defaults) via map:getBasemapStyles and switches with map:setBasemap — deck.gl swaps the vector style in place; Leaflet rebuilds the tile layer.

Measure

Subscribes to map:click / map:mousemove, collects two points, and draws the line + endpoints as a vector layer via map:createLayer. Distance is computed with Turf; the label is positioned by projecting the segment midpoint via map:latLngToContainerPoint.

Zoom

map:zoomIn / map:zoomOut, clamped to the engine's min/max zoom.

Dependency on #90 (imapengine-drawing)

Vector overlays (the measure line and the search pin) are drawn via map:createLayer / map:removeLayer, which are provided by #90. Until #90 merges these two features no-op (guarded, no crash); the rest of the plugin is self-contained. See #115 for the full rationale on why this uses map:createLayer rather than its own overlay channels.

Known limitation / future work

MapControl is a floating overlay, not a docked panel, so it bypasses the normal panel-mount path: it self-mounts at bundle load by polling for the map container and rendering into a position:fixed layer on document.body. This works but should be replaced by a proper "floating tool" mount path in the Modern layout so overlays don't have to self-mount.

Testing

Unit suite and npm run build pass on the stacked branch. Manual checks (from #115):

• Toggle each of the four features from the Configure page; confirm each appears/hides.
• Test on both a Leaflet and a deck.gl mission.
• Basemap switcher: confirm the list populates (it retries until the map registers its handlers) and switching restyles the map on both engines.
• Search: type a place, confirm results, select one, confirm fly-to + pin.
• Measure: click two points, confirm line + distance label. (Requires feat(core): drawing primitives + overlay + bus surface on IMapEngine #90 for the overlay.)
• Zoom: confirm in/out and that it stops at min/max.