fix(export): clear timeline selection when opening export panel

When a zoom/trim/speed region is selected, hasTimelineSelection is true
and the export panel is gated behind !hasTimelineSelection. Clicking the
Download button only switched activePanelMode locally in SettingsPanel
without clearing the selection in VideoEditor, so the export panel never
rendered.

Add onExportPanelOpen callback prop to SettingsPanel and call it on
Download button click to clear selectedZoomId, selectedTrimId, and
selectedSpeedId — making hasTimelineSelection false and unblocking the
export panel.

Complements PR #611 which fixed the bulk suggest-zooms path; this
covers the manual selection path.

src/components/video-editor/SettingsPanel.tsx

@@ -284,6 +284,7 @@ interface SettingsPanelProps {
 	onGifSizePresetChange?: (preset: GifSizePreset) => void;
 	gifOutputDimensions?: { width: number; height: number };
 	onExport?: () => void;
+	onExportPanelOpen?: () => void;
 	unsavedExport?: {
 		arrayBuffer: ArrayBuffer;
 		fileName: string;
@@ -414,6 +415,7 @@ export function SettingsPanel({
 	onGifSizePresetChange,
 	gifOutputDimensions = DEFAULT_GIF_SETTINGS.outputDimensions,
 	onExport,
+	onExportPanelOpen,
 	unsavedExport,
 	onSaveUnsavedExport,
 	selectedAnnotationId,
@@ -822,7 +824,10 @@ export function SettingsPanel({
 						data-testid={getTestId("export-panel-button")}
 						type="button"
 						title={exportPanelMode.label}
-						onClick={() => setActivePanelMode(exportPanelMode.id)}
+						onClick={() => {
+							setActivePanelMode(exportPanelMode.id);
+							onExportPanelOpen?.();
+						}}
 						className={cn(
 							"mt-auto flex h-8 w-8 items-center justify-center rounded-lg border transition-all",
 							activePanelMode === "export" && !hasTimelineSelection

src/components/video-editor/VideoEditor.tsx

@@ -2256,6 +2256,11 @@ export default function VideoEditor() {
 											: getAspectRatioValue(aspectRatio),
 									)}
 									onExport={handleOpenExportDialog}
+									onExportPanelOpen={() => {
+										setSelectedZoomId(null);
+										setSelectedTrimId(null);
+										setSelectedSpeedId(null);
+									}}
 									selectedAnnotationId={selectedAnnotationId}
 									annotationRegions={annotationOnlyRegions}
 									onAnnotationContentChange={handleAnnotationContentChange}