fix(stammbaum): anchor fresh visit to content top-left, drop space above row 1 (#692)

The frame-corner anchor + xMidYMid letterboxing left ~290px of empty space
above the first row on desktop. Anchor to the content corner (first row /
leftmost node, small margin) via cornerView, and switch the canvas to
xMinYMin meet so a wide/short tree pins to the top-left instead of centring
vertically. Verified live: gap above row 1 is now ~20px.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/person/genealogy/StammbaumTree.svelte

@@ -12,8 +12,9 @@ import {
 import {
 	type PanZoomState,
 	clampZoom,
+	clampPan,
 	recentreOn,
-	topLeftView,
+	cornerView,
 	ZOOM_STEP_KB
 } from '$lib/person/genealogy/panZoom';
 import { panZoomGestures } from '$lib/person/genealogy/panZoomGestures';
@@ -143,10 +144,30 @@ const railRows = $derived(
 		.map((r) => ({ rank: r.rank, label: r.label, centerY: r.y + NODE_H / 2 }))
 );
 
-// A fresh visit (no shared URL state) lands on the tree's top-left corner rather
-// than its centre (#692). Runs once after layout is available.
+// A fresh visit (no shared URL state) lands on the tree's content top-left
+// rather than its centre (#692). Anchors to the first row / leftmost node (not
+// the padded frame corner, which would leave empty space above row 1), with a
+// small margin. Runs once after layout is available.
+const ANCHOR_MARGIN = 24;
 onMount(() => {
-	if (anchorTopLeft) onPanZoom(topLeftView(baseDims.w, baseDims.h, panZoom.z));
+	if (!anchorTopLeft) return;
+	let minX = Infinity;
+	let minY = Infinity;
+	for (const pos of layout.positions.values()) {
+		minX = Math.min(minX, pos.x);
+		minY = Math.min(minY, pos.y);
+	}
+	if (!Number.isFinite(minX)) return; // no nodes
+	const target = cornerView(
+		minX - ANCHOR_MARGIN,
+		minY - ANCHOR_MARGIN,
+		baseCentre.x,
+		baseCentre.y,
+		baseDims.w,
+		baseDims.h,
+		panZoom.z
+	);
+	onPanZoom(clampPan(target, baseDims.w, baseDims.h));
 });
 
 const viewBox = $derived.by(() => {
@@ -309,7 +330,7 @@ const parentLinks = $derived.by<ParentLinks>(() => {
 	<svg
 		bind:this={svgEl}
 		viewBox={viewBox}
-		preserveAspectRatio="xMidYMid meet"
+		preserveAspectRatio="xMinYMin meet"
 		role="img"
 		aria-label="Stammbaum"
 		tabindex="0"

frontend/src/lib/person/genealogy/panZoom.test.ts

@@ -9,7 +9,7 @@ import {
 	stepInertia,
 	recentreOn,
 	clampPan,
-	topLeftView,
+	cornerView,
 	lerpView,
 	DEFAULT_VIEW,
 	DEFAULT_ZOOM,
@@ -208,15 +208,17 @@ describe('clampPan', () => {
 	});
 });
 
-describe('topLeftView', () => {
-	it('aligns the viewBox top-left with the tree corner at the given zoom', () => {
-		expect(topLeftView(1000, 800, 2)).toEqual({ x: -250, y: -200, z: 2 });
+describe('cornerView', () => {
+	// Frame 0..1000 × 0..800, centre (500, 400).
+	it('puts the viewBox top-left on the target SVG point', () => {
+		// Target = content top-left at (100, 80), z=2 → viewBox is 500×400.
+		expect(cornerView(100, 80, 500, 400, 1000, 800, 2)).toEqual({ x: -150, y: -120, z: 2 });
 	});
 
-	it('sits exactly at the negative clamp limit (the corner is reachable)', () => {
-		const v = topLeftView(1000, 800, 3);
-		// clampPan must leave the corner view untouched (it is on the boundary).
-		expect(clampPan(v, 1000, 800)).toEqual(v);
+	it('reduces to the frame corner when the target is the frame top-left', () => {
+		// Target = frame top-left (0, 0) → most-negative (corner) pan.
+		const v = cornerView(0, 0, 500, 400, 1000, 800, 3);
+		expect(clampPan(v, 1000, 800)).toEqual(v); // on the clamp boundary
 	});
 });
 

frontend/src/lib/person/genealogy/panZoom.ts

@@ -196,12 +196,25 @@ export function clampPan(state: PanZoomState, baseW: number, baseH: number): Pan
 }
 
 /**
- * The view whose viewBox top-left aligns with the tree's top-left corner at zoom
- * `z` (the landing view for a fresh visit). This is the pan at the most-negative
- * edge of the pannable range, i.e. `-clampPan` limit on each axis.
+ * The view whose viewBox top-left lands on the SVG point (`targetX`, `targetY`)
+ * at zoom `z` — used to anchor a fresh visit to the tree's content corner.
+ * Pass the content bounding-box top-left (not the padded frame corner) so the
+ * first row sits near the top with no empty slack above it.
  */
-export function topLeftView(baseW: number, baseH: number, z: number): PanZoomState {
-	return { x: (baseW / z - baseW) / 2, y: (baseH / z - baseH) / 2, z };
+export function cornerView(
+	targetX: number,
+	targetY: number,
+	baseCentreX: number,
+	baseCentreY: number,
+	baseW: number,
+	baseH: number,
+	z: number
+): PanZoomState {
+	return {
+		x: targetX - baseCentreX + baseW / z / 2,
+		y: targetY - baseCentreY + baseH / z / 2,
+		z
+	};
 }
 
 /**