feat: v0.1.4 — device intelligence dashboard

Add tabbed dashboard at /dashboard/ with three D3.js visualizations:
- Vendor treemap (devices grouped by type and vendor)
- SSID social graph (force-directed, shared probed SSIDs as edges)
- Fingerprint clusters (packed circles by device behavior)

Intelligence API endpoints at /api/v1/intelligence/ with param
validation. Dashboard built on htmx + Pico CSS dark theme + D3 v7,
all vendored locally (make vendor). 13 new tests (59 total).

static/js/main.js

@@ -0,0 +1,58 @@
+/* ESP32-Web Dashboard — tab switching & shared utilities */
+
+document.addEventListener('DOMContentLoaded', () => {
+  initTabs();
+});
+
+function initTabs() {
+  const tabs = document.querySelectorAll('.tab-nav a');
+  tabs.forEach(tab => {
+    tab.addEventListener('click', (e) => {
+      e.preventDefault();
+      if (tab.classList.contains('active')) return;
+      tabs.forEach(t => t.classList.remove('active'));
+      tab.classList.add('active');
+      // htmx handles the AJAX load via hx-get on the element
+    });
+  });
+
+  // Load first tab on page load
+  const first = document.querySelector('.tab-nav a');
+  if (first) {
+    first.click();
+  }
+}
+
+/* Shared D3 tooltip */
+function createTooltip() {
+  let tip = document.querySelector('.d3-tooltip');
+  if (!tip) {
+    tip = document.createElement('div');
+    tip.className = 'd3-tooltip';
+    tip.style.display = 'none';
+    document.body.appendChild(tip);
+  }
+  return {
+    show(html, event) {
+      tip.innerHTML = html;
+      tip.style.display = 'block';
+      tip.style.left = (event.pageX + 12) + 'px';
+      tip.style.top = (event.pageY - 12) + 'px';
+    },
+    move(event) {
+      tip.style.left = (event.pageX + 12) + 'px';
+      tip.style.top = (event.pageY - 12) + 'px';
+    },
+    hide() {
+      tip.style.display = 'none';
+    }
+  };
+}
+
+/* Responsive SVG dimensions from container */
+function getVizSize(container) {
+  return {
+    width: Math.max(container.clientWidth || container.parentElement.clientWidth, 300),
+    height: Math.max(container.clientHeight, 400)
+  };
+}