phase 2-6: complete D3/TopoJSON migration

Replace ZingChart + jQuery with D3 v7 + TopoJSON. Implements all
planned phases: choropleth map (NaturalEarth1 projection, YlOrRd
gradient), hover tooltip, zoom/pan/reset, country detail modal,
side-by-side compare, metric selector, label toggle, donut pie chart
with per-country drilldown bar chart. Upgrades Bootstrap JS bundle
from v4.5.3 (jQuery-dependent) to v5.0.0, fixes modal API calls
to use getInstance/constructor pattern compatible with BS 5.0.0+.
Removes jquery, zingchart ×3 library files.

1 files changed, 29 insertions, 3 deletions

diff --git a/assets/js/map/tooltip.js b/assets/js/map/tooltip.js
index c8f112a..c74418b 100644
--- a/assets/js/map/tooltip.js
+++ b/assets/js/map/tooltip.js
@@ -1,3 +1,29 @@
-// Phase 3: hover tooltip
-export function initTooltip() {}
-export function attachTooltip(selection, getContent) {}
+import * as d3 from "https://cdn.jsdelivr.net/npm/d3@7/+esm";
+
+let tooltip;
+
+export function initTooltip() {
+	tooltip = d3.select("body")
+		.append("div")
+		.attr("class", "map-tooltip");
+}
+
+export function attachTooltip(selection, getContent) {
+	selection
+		.on("mouseover", (event, d) => {
+			const content = getContent(event, d);
+			if (content) {
+				tooltip.style("opacity", 1).html(content);
+			} else {
+				tooltip.style("opacity", 0);
+			}
+		})
+		.on("mousemove", (event) => {
+			tooltip
+				.style("left", (event.pageX + 12) + "px")
+				.style("top", (event.pageY - 28) + "px");
+		})
+		.on("mouseout", () => {
+			tooltip.style("opacity", 0);
+		});
+}