feat(network-visualiser): add utility functions for trail positioning and view bounds, and define visualiser constants

meshchatx/src/frontend/components/network-visualiser/internal/trailUtils.js

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+export function getPositionAlongTrail(trail, distBehind) {
+    if (!trail || trail.length === 0) return { x: 0, y: 0 };
+    if (trail.length === 1) return { ...trail[0] };
+    let d = 0;
+    for (let i = trail.length - 1; i > 0; i--) {
+        const p = trail[i];
+        const q = trail[i - 1];
+        const seg = Math.hypot(p.x - q.x, p.y - q.y);
+        if (d + seg >= distBehind) {
+            const t = seg > 0 ? (distBehind - d) / seg : 0;
+            return { x: p.x + (q.x - p.x) * t, y: p.y + (q.y - p.y) * t };
+        }
+        d += seg;
+    }
+    return { ...trail[0] };
+}

meshchatx/src/frontend/components/network-visualiser/internal/viewBounds.js

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+export function getViewCanvasBounds(network) {
+    const container = document.getElementById("network");
+    if (!container || !network) return null;
+    const scale = network.getScale();
+    const vp = network.getViewPosition();
+    const w = container.clientWidth;
+    const h = container.clientHeight;
+    const halfW = w / (2 * scale);
+    const halfH = h / (2 * scale);
+    return {
+        left: vp.x - halfW,
+        right: vp.x + halfW,
+        top: vp.y - halfH,
+        bottom: vp.y + halfH,
+        scale,
+    };
+}

meshchatx/src/frontend/components/network-visualiser/internal/visualiserConstants.js

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+export const PONG_NODE_IDS = ["__pong_ball", "__pong_pad_l", "__pong_pad_r", "__pong_hud"];