Initial commit: webtrees full diagram chart module

Interactive SVG family tree visualization using ELK (Sugiyama) for
layout and D3 for rendering. Shows ancestors, descendants, and siblings
in a single diagram with orthogonal bus-line connectors.

Features:
- Bidirectional tree traversal (ancestors + descendants + siblings)
- Generation-aligned layout with post-processing Y-snap
- Person cards with photos, names, dates, and hover bio cards
- "More ancestors" indicator for persons with hidden parents
- Pan/zoom navigation
- Docker dev environment

resources/js/modules/lib/tree/link-drawer.js

@@ -0,0 +1,31 @@
+/**
+ * Link/connector drawing utilities.
+ *
+ * Uses elbow (right-angle) connectors for a clean genealogy look.
+ */
+
+/**
+ * Draw an elbow link between source and target nodes.
+ *
+ * @param {d3.Selection} group - SVG group to append the path to
+ * @param {object} source - Source node with x, y coordinates
+ * @param {object} target - Target node with x, y coordinates
+ * @param {string} cssClass - Additional CSS class for the link
+ * @param {Configuration} config
+ */
+export function drawElbowLink(group, source, target, cssClass, config) {
+    const halfHeight = config.cardHeight / 2;
+
+    // Midpoint Y between source and target
+    const midY = (source.y + target.y) / 2;
+
+    const path = `M ${source.x} ${source.y + (target.y > source.y ? halfHeight : -halfHeight)}
+                  L ${source.x} ${midY}
+                  L ${target.x} ${midY}
+                  L ${target.x} ${target.y + (target.y > source.y ? -halfHeight : halfHeight)}`;
+
+    group
+        .append("path")
+        .attr("class", `link ${cssClass}`)
+        .attr("d", path);
+}