Zoom-reset ankret til viewport-sentrum

Reset til 100% justerer kameraposisjon slik at det du ser i
midten forblir i midten. Gjelder dobbeltklikk og toolbar-knapp.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/canvas/Canvas.svelte

@@ -426,6 +426,18 @@
 		};
 	}
 
+	// --- Reset zoom (ankret til viewport-sentrum) ---
+	function resetZoom() {
+		const cx = viewport.width / 2;
+		const cy = viewport.height / 2;
+		const scale = 1.0 / camera.zoom;
+		camera = {
+			x: cx - scale * (cx - camera.x),
+			y: cy - scale * (cy - camera.y),
+			zoom: 1.0,
+		};
+	}
+
 	// --- Fullscreen ---
 	function toggleFullscreen() {
 		isFullscreen = !isFullscreen;
@@ -478,7 +490,7 @@
 	ondblclick={(e) => {
 		if (!(e.target as HTMLElement).closest('[data-canvas-object-id]') &&
 			!(e.target as HTMLElement).closest('.canvas-toolbar')) {
-			camera = { ...camera, zoom: 1.0 };
+			resetZoom();
 		}
 	}}
 	ontouchstart={handleTouchStart}
@@ -496,7 +508,7 @@
 			title="Zoom ut (−15%)"
 			aria-label="Zoom ut"
 		>−</button>
-		<button class="canvas-toolbar-zoom" onclick={() => { camera = { ...camera, zoom: 1.0 }; }} title="Tilbakestill til 100%">{Math.round(camera.zoom * 100)}%</button>
+		<button class="canvas-toolbar-zoom" onclick={() => { resetZoom(); }} title="Tilbakestill til 100%">{Math.round(camera.zoom * 100)}%</button>
 		<button
 			class="canvas-toolbar-btn"
 			onclick={() => zoomStep(0.15)}