Fix ticket age, bulk assign, add column visibility toggle

- TicketView: ticket age was measuring from last update not creation;
  fixed to always use created_at
- dashboard.js: bulk assign used non-existent onSelect callback (no
  selection was ever stored); fixed to onChange with selected[0],
  added max:1 to enforce single-select
- base.js: lt.combobox Enter key only fired when focusedIdx >= 0;
  now falls back to first filtered result when no arrow key used
- DashboardView + dashboard.js + dashboard.css: add COLS ▾ button on
  table header that opens a checkbox panel to show/hide optional
  columns (Ticket ID, Category, Type, Created By, Assigned To,
  Created, Updated); state persisted in localStorage, Reset button
  restores all; core columns (Priority, Title, Status, Actions) always
  visible; data-col attributes added to all th/td for CSS targeting

Notifications bell: was functional all along — was broken by the
notifications.php 500 error (now fixed). Avg resolution: correct,
tickets genuinely take ~158 days average on this dataset.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

assets/js/dashboard.js

@@ -603,7 +603,8 @@ function showBulkAssignModal() {
                     label: u.display_name || u.username
                 }));
                 lt.combobox.init(input, items, {
-                    onSelect: function(item) { _bulkAssignUserId = item.value; }
+                    max: 1,
+                    onChange: function(selected) { _bulkAssignUserId = selected[0] || null; }
                 });
             }
         })
@@ -1543,3 +1544,78 @@ setInterval(initRelativeTimes, 60000);
 // Export for use in other scripts
 window.showLoadingOverlay = showLoadingOverlay;
 window.hideLoadingOverlay = hideLoadingOverlay;
+
+// ── Column visibility toggle ──────────────────────────────────────
+(function initColToggle() {
+    const LS_KEY = 'lt_col_visibility';
+
+    function getHidden() {
+        try { return JSON.parse(localStorage.getItem(LS_KEY) || '[]'); } catch(_) { return []; }
+    }
+    function saveHidden(cols) {
+        try { localStorage.setItem(LS_KEY, JSON.stringify(cols)); } catch(_) {}
+    }
+
+    function applyVisibility(hidden) {
+        const table = document.getElementById('tickets-table');
+        if (!table) return;
+        // All toggleable columns
+        const all = ['ticket_id','category','type','created_by','assigned_to','created_at','updated_at'];
+        all.forEach(col => {
+            const vis = !hidden.includes(col);
+            table.querySelectorAll('[data-col="' + col + '"]').forEach(el => {
+                el.style.display = vis ? '' : 'none';
+            });
+        });
+        // Update checkboxes
+        document.querySelectorAll('.col-toggle-cb').forEach(cb => {
+            cb.checked = !hidden.includes(cb.dataset.col);
+        });
+    }
+
+    document.addEventListener('DOMContentLoaded', function() {
+        const btn   = document.getElementById('colToggleBtn');
+        const panel = document.getElementById('colTogglePanel');
+        const reset = document.getElementById('colToggleReset');
+        if (!btn || !panel) return;
+
+        // Apply saved state on load
+        applyVisibility(getHidden());
+
+        // Toggle panel open/close
+        btn.addEventListener('click', function(e) {
+            e.stopPropagation();
+            const open = panel.getAttribute('aria-hidden') === 'false';
+            panel.setAttribute('aria-hidden', open ? 'true' : 'false');
+            btn.setAttribute('aria-expanded', open ? 'false' : 'true');
+            btn.textContent = (open ? 'COLS \u25BE' : 'COLS \u25B4');
+        });
+
+        // Close on outside click
+        document.addEventListener('click', function(e) {
+            if (!btn.contains(e.target) && !panel.contains(e.target)) {
+                panel.setAttribute('aria-hidden', 'true');
+                btn.setAttribute('aria-expanded', 'false');
+                btn.textContent = 'COLS \u25BE';
+            }
+        });
+
+        // Checkbox change
+        panel.addEventListener('change', function(e) {
+            if (!e.target.classList.contains('col-toggle-cb')) return;
+            const hidden = Array.from(document.querySelectorAll('.col-toggle-cb'))
+                .filter(cb => !cb.checked)
+                .map(cb => cb.dataset.col);
+            saveHidden(hidden);
+            applyVisibility(hidden);
+        });
+
+        // Reset
+        if (reset) {
+            reset.addEventListener('click', function() {
+                saveHidden([]);
+                applyVisibility([]);
+            });
+        }
+    });
+})();