Eng-council sweep: export hygiene, dead code, helper dedup, declare vega-expression

src/app/services/chart-renderer.ts

@@ -12,7 +12,7 @@ import type { VisualizationSpec } from 'vega-embed';
 import type { Config } from 'vega-lite';
 
 /** Options for `RenderHandle.toImageURL` (spec §08 → Per-chart export). */
-export interface ImageExportOptions {
+interface ImageExportOptions {
   /**
    * Pixel-density multiplier for the **PNG** raster, **relative to the device**.
    * The image is drawn at `scale × devicePixelRatio` logical-pixel density, so
@@ -80,7 +80,7 @@ export interface RenderOptions {
  * size against this (÷ dpr, since the backing store is dpr× the CSS size) and
  * throws `ChartTooLargeError` rather than handing back a blank canvas.
  */
-export const MAX_CANVAS_PX = 32767;
+const MAX_CANVAS_PX = 32767;
 
 /**
  * Thrown by `renderSpec` when a **canvas**-backed chart resolves to a height larger