feat(d3): implement swarm-basic (#9946)

## Implementation: `swarm-basic` - javascript/d3

Implements the **javascript/d3** version of `swarm-basic`.

**File:** `plots/swarm-basic/implementations/javascript/d3.js`

**Parent Issue:** #974

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/30192549742)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Markus Neusinger <2921697+MarkusNeusinger@users.noreply.github.com>

Author: github-actions[bot]

plots/swarm-basic/implementations/javascript/d3.js

@@ -0,0 +1,156 @@
+// anyplot.ai
+// swarm-basic: Basic Swarm Plot
+// Library: d3 7.9.0 | JavaScript 22.23.1
+// Quality: 92/100 | Created: 2026-07-26
+
+const t = window.ANYPLOT_TOKENS;
+const { width, height } = window.ANYPLOT_SIZE;
+const margin = { top: 110, right: 60, bottom: 90, left: 110 };
+const iw = width - margin.left - margin.right;
+const ih = height - margin.top - margin.bottom;
+
+// --- Data (in-memory, deterministic, fixed-seed LCG) ------------------------
+let seed = 42;
+function lcgUniform() {
+  seed = (seed * 1664525 + 1013904223) % 4294967296;
+  return seed / 4294967296;
+}
+function gaussian(mean, sd) {
+  const u1 = Math.max(lcgUniform(), 1e-9);
+  const u2 = lcgUniform();
+  const z = Math.sqrt(-2 * Math.log(u1)) * Math.cos(2 * Math.PI * u2);
+  return mean + z * sd;
+}
+
+const groups = [
+  { category: "Placebo", mean: 8.2, sd: 2.1, n: 42 },
+  { category: "Low Dose", mean: 6.4, sd: 1.9, n: 45 },
+  { category: "Medium Dose", mean: 4.6, sd: 1.7, n: 44 },
+  { category: "High Dose", mean: 3.1, sd: 1.4, n: 40 },
+];
+
+const data = [];
+for (const grp of groups) {
+  for (let i = 0; i < grp.n; i++) {
+    data.push({ category: grp.category, value: Math.max(0.3, gaussian(grp.mean, grp.sd)) });
+  }
+}
+const categories = groups.map((grp) => grp.category);
+
+// --- Scales -------------------------------------------------------------
+// Domain hugs the data range (not zero-anchored) — a swarm reads individual
+// values, not magnitude-from-zero, so a tight domain uses the canvas fully.
+const dataMin = d3.min(data, (d) => d.value);
+const dataMax = d3.max(data, (d) => d.value);
+const pad = (dataMax - dataMin) * 0.08;
+const x = d3.scaleBand().domain(categories).range([0, iw]).padding(0.18);
+const y = d3
+  .scaleLinear()
+  .domain([Math.max(0, dataMin - pad), dataMax + pad])
+  .nice()
+  .range([ih, 0]);
+const color = d3.scaleOrdinal().domain(categories).range(t.palette);
+
+// --- Beeswarm layout (force simulation, settled synchronously) --------------
+// `fy` pins each node's vertical position exactly to its value — only x is
+// free, so the simulation resolves overlap purely by spreading horizontally
+// (a `forceY` pull instead of a fixed `fy` lets collide drag points off the
+// value line entirely, even clipping them off-canvas at high density).
+const radius = 7;
+const nodes = data.map((d) => ({
+  ...d,
+  targetX: x(d.category) + x.bandwidth() / 2,
+  fy: y(d.value),
+}));
+
+const simulation = d3
+  .forceSimulation(nodes)
+  .force("x", d3.forceX((d) => d.targetX).strength(0.15))
+  .force("collide", d3.forceCollide(radius + 0.6))
+  .stop();
+for (let i = 0; i < 300; i++) simulation.tick();
+
+// Keep points within their own band so groups never bleed into neighbors.
+for (const n of nodes) {
+  const lo = x(n.category) + radius;
+  const hi = x(n.category) + x.bandwidth() - radius;
+  n.x = Math.min(hi, Math.max(lo, n.x));
+}
+
+// --- SVG mount ----------------------------------------------------------
+const svg = d3.select("#container").append("svg").attr("width", width).attr("height", height);
+const g = svg.append("g").attr("transform", `translate(${margin.left},${margin.top})`);
+
+// --- Gridlines (y-axis only, subtle) -----------------------------------
+g.append("g")
+  .call(d3.axisLeft(y).ticks(6).tickSize(-iw).tickFormat(""))
+  .call((sel) => sel.select(".domain").remove())
+  .selectAll("line")
+  .attr("stroke", t.grid);
+
+// --- Median markers per category (drawn under the points) -------------------
+const markerHalfWidth = 70;
+for (const cat of categories) {
+  const values = data.filter((d) => d.category === cat).map((d) => d.value);
+  const median = d3.median(values);
+  const cx = x(cat) + x.bandwidth() / 2;
+  g.append("line")
+    .attr("x1", cx - markerHalfWidth)
+    .attr("x2", cx + markerHalfWidth)
+    .attr("y1", y(median))
+    .attr("y2", y(median))
+    .attr("stroke", t.ink)
+    .attr("stroke-width", 2.5)
+    .attr("stroke-opacity", 0.55)
+    .attr("stroke-linecap", "round");
+}
+
+// --- Points -------------------------------------------------------------
+g.selectAll("circle")
+  .data(nodes)
+  .join("circle")
+  .attr("cx", (d) => d.x)
+  .attr("cy", (d) => d.y)
+  .attr("r", radius)
+  .attr("fill", (d) => color(d.category))
+  .attr("fill-opacity", 0.85)
+  .attr("stroke", t.pageBg)
+  .attr("stroke-width", 1);
+
+// --- Axes -----------------------------------------------------------------
+const xAxis = g.append("g").attr("transform", `translate(0,${ih})`).call(d3.axisBottom(x).tickSizeOuter(0));
+const yAxis = g.append("g").call(d3.axisLeft(y).ticks(6));
+for (const ax of [xAxis, yAxis]) {
+  ax.selectAll("text").attr("fill", t.inkSoft).style("font-size", "14px");
+  ax.selectAll(".tick line").remove();
+  ax.select(".domain").attr("stroke", t.inkSoft);
+}
+
+// --- Axis labels ------------------------------------------------------------
+g.append("text")
+  .attr("x", iw / 2)
+  .attr("y", ih + 64)
+  .attr("text-anchor", "middle")
+  .attr("fill", t.ink)
+  .style("font-size", "16px")
+  .text("Treatment Group");
+
+g.append("text")
+  .attr("transform", "rotate(-90)")
+  .attr("x", -ih / 2)
+  .attr("y", -78)
+  .attr("text-anchor", "middle")
+  .attr("fill", t.ink)
+  .style("font-size", "16px")
+  .text("CRP Biomarker Level (mg/L)");
+
+// --- Title --------------------------------------------------------------
+svg
+  .append("text")
+  .attr("x", width / 2)
+  .attr("y", 56)
+  .attr("text-anchor", "middle")
+  .attr("fill", t.ink)
+  .style("font-size", "22px")
+  .style("font-weight", "600")
+  .text("swarm-basic · javascript · d3 · anyplot.ai");