feat(core): drawing primitives + overlay + bus surface on IMapEngine

[BhattaraiSijan]

Adds to the core map engine + plugin bus. Consumed downstream by a follow-up AOI plugin PR

Drawing

• IMapEngine: 4 methods (enableDrawing / disableDrawing / finishDrawing / isDrawing) + 4 events (drawstart / drawvertex / drawcomplete / drawcancel).
• types/events.ts: 6 types — DrawShape, DrawingOptions, and 4 event payload interfaces.
• Leaflet adapter: wraps leaflet-draw + 2 helpers in LeafletHelpers.ts (leafletDrawnLayerToFeature, extractDrawVertices).
• DeckGL adapter: hand-rolled state machine + 3 helpers in DeckGLHelpers.ts (buildDrawnFeature, buildPreviewFeature, 32-segment circle approximation + haversine for radius).

Anchored HTML overlays

• IMapEngine: 2 methods (addOverlay / removeOverlay) + 1 type (OverlayOptions).
• Leaflet adapter: backed by L.marker + L.divIcon (reposition is native).
• DeckGL adapter: DOM node appended to the container, reprojected on move / moveend.

Bus surface in Map_.js

• Refactored 6 existing providers (map:getCenter / getBounds / getZoom / setView / fitBounds / panTo) from Map_.map.* → engine.* so they're engine-agnostic.
• Added 9 providers: drawing (4) + layers (createLayer / removeLayer / hasLayer, wrapping pre-existing engine methods) + overlays (2).
• Added 6 engine → bus re-emits: 4 drawing events + move / moveend.

MapEngines/index.ts exports the new types.

Follow-up: consumer plugin PR

The AOI plugin PR (feat/draw-aoi-plugin) consumes this surface:

• mmgisAPI.request('map:enableDrawing', ...) for the draw flow.
• mmgisAPI.on('map:drawcomplete', ...) to receive the finalised feature.
• mmgisAPI.request('map:createLayer', ...) to render the selected AOI on the map.
• mmgisAPI.request('map:addOverlay', ...) for the action tooltip.

No further core changes are required for that PR to ship.

Discussion

• **DeckGL draw is hand-rolled ** vs Leaflet's thin wrapper around leaflet-draw. Maybe use library like terradraw for deck.gl drawing? Experimented with editable-layers, but it did not work.
• Branch history includes the editable-layers experiment + revert (1c9b1751 / 40c0a899). Recommend squash-and-merge to keep development's log clean.

Closes: #88

Test plan

• Polygon / rectangle / circle draw flow in Leaflet and DeckGL overlay mode — verified manually with the AOI plugin on feat/draw-aoi-plugin.
• AOI plugin tooltip mounted via map:addOverlay, removed via map:removeOverlay.
• map:drawcomplete payload reaches a consumer plugin through the bus.
• npx tsc --noEmit exits 0.