Merge #22 chart click-to-filter into main

All three charts (priority donut, status donut, category bar) now navigate to
the same URL filters the stat cards already use, with a pointer cursor on
hover, a title hint, and "click to filter" in the tooltip.

The status each click applies is explicit rather than left to the default. With
no `status` param the controller falls back to the viewer's
default_status_filters preference, which can be anything, so the list would not
necessarily match what the chart counted. StatsModel builds by_priority and
by_category with `status != 'Closed'` while by_status spans every status, so
only the priority and category charts pin the open set; the status chart filters
on the clicked status alone (which is how clicking "Closed" works at all).

Verified two ways:
- 17/17 in headless chromium, driving the real chart script from this view with
  the Chart constructor stubbed, asserting the exact query each click produces
  and that a click hitting no segment navigates nowhere.
- Against the live database, every segment's count equals the number of tickets
  its filter returns — 12/12 across all three charts — so the list you land on
  matches the number you clicked.

views/DashboardView.php

@@ -277,9 +277,64 @@ include __DIR__ . '/layout_header.php';
       array_values($stats['by_category'] ?? [])
   ))) ?>;
 
+  // ── Click-to-filter ────────────────────────────────────────────────────────
+  // Charts navigate to the same URL filters the stat cards use.
+  //
+  // The status the click filters on has to be explicit rather than left to the
+  // default: with no `status` param the controller falls back to the viewer's
+  // default_status_filters preference, which can be anything, so the resulting
+  // list would not necessarily match what the chart counted. StatsModel builds
+  // by_priority and by_category with `status != 'Closed'`, while by_status spans
+  // every status — so only the priority and category charts pin the open set.
+  function openStatuses() {
+    var all = window.TICKET_STATUSES || ['Open', 'Pending', 'In Progress', 'Closed'];
+    return all.filter(function(s) { return s !== 'Closed'; }).join(',');
+  }
+
+  function gotoFilter(params) {
+    var qs = new URLSearchParams();
+    Object.keys(params).forEach(function(k) {
+      if (params[k] !== null && params[k] !== undefined && params[k] !== '') qs.set(k, params[k]);
+    });
+    window.location.href = '/?' + qs.toString();
+  }
+
+  // Each chart maps a clicked label to a filter. Returns null when the label
+  // can't be mapped, so the click is simply ignored.
+  var CHART_FILTERS = {
+    chartPriority: function(label) {
+      var m = /^P(\d+)$/.exec(label);
+      return m ? { priority: m[1], status: openStatuses() } : null;
+    },
+    chartStatus: function(label) {
+      return label ? { status: label } : null;
+    },
+    chartCategory: function(label) {
+      return label ? { category: label, status: openStatuses() } : null;
+    }
+  };
+
+  function filterOnClick(canvasId) {
+    return function(evt, elements, chart) {
+      if (!elements || !elements.length) return;
+      var label = chart.data.labels[elements[0].index];
+      var mapper = CHART_FILTERS[canvasId];
+      var params = mapper && mapper(label);
+      if (params) gotoFilter(params);
+    };
+  }
+
+  // Pointer cursor over clickable segments so the affordance is visible.
+  function filterOnHover(evt, elements) {
+    if (evt && evt.native && evt.native.target) {
+      evt.native.target.style.cursor = (elements && elements.length) ? 'pointer' : 'default';
+    }
+  }
+
   function makeDonut(canvasId, data, colorMap) {
     var ctx = document.getElementById(canvasId);
     if (!ctx || !data.length) return;
+    ctx.title = 'Click a segment to filter the ticket list';
     return new Chart(ctx, {
       type: 'doughnut',
       data: {
@@ -295,12 +350,14 @@ include __DIR__ . '/layout_header.php';
       },
       options: {
         responsive: true, maintainAspectRatio: false,
+        onClick: filterOnClick(canvasId),
+        onHover: filterOnHover,
         plugins: {
           legend: {
             position: 'bottom',
             labels: { color: '#8fa3b1', font: { family: 'monospace', size: 10 }, padding: 8, boxWidth: 10 }
           },
-          tooltip: { callbacks: { label: function(ctx) { return ' ' + ctx.label + ': ' + ctx.parsed; } } }
+          tooltip: { callbacks: { label: function(ctx) { return ' ' + ctx.label + ': ' + ctx.parsed + ' — click to filter'; } } }
         },
         cutout: '68%'
       }
@@ -310,6 +367,7 @@ include __DIR__ . '/layout_header.php';
   function makeBar(canvasId, data) {
     var ctx = document.getElementById(canvasId);
     if (!ctx || !data.length) return;
+    ctx.title = 'Click a bar to filter the ticket list';
     return new Chart(ctx, {
       type: 'bar',
       data: {
@@ -323,7 +381,12 @@ include __DIR__ . '/layout_header.php';
       },
       options: {
         indexAxis: 'y', responsive: true, maintainAspectRatio: false,
-        plugins: { legend: { display: false } },
+        onClick: filterOnClick(canvasId),
+        onHover: filterOnHover,
+        plugins: {
+          legend: { display: false },
+          tooltip: { callbacks: { label: function(ctx) { return ' ' + ctx.parsed.x + ' — click to filter'; } } }
+        },
         scales: {
           x: { ticks: { color: '#8fa3b1', font: { size: 10 } }, grid: { color: 'rgba(0,255,65,0.06)' } },
           y: { ticks: { color: '#8fa3b1', font: { family: 'monospace', size: 10 } }, grid: { display: false } }