Replace the mobile tab bar with a hamburger menu

Six tabs (Queue, On-call, Alerts, Team, Admin, Account) had already
outgrown the bottom bar once: 56b8191 let it auto-size its columns to
fit however many there were, but on a phone that only left each tab
55-65px wide. Squeezing further wasn't an option, so the bar is gone
on mobile and a hamburger button in the topbar opens a menu instead.

The menu reuses the sheet + menu-item pattern already used for the
snooze and assign-to actions in incident.js, rather than a new overlay
component. It lists the same sections the sidebar does, including
hiding Admin for non-admins, and the triggered-incident badge that
used to sit on the Queue tab icon now shows on the hamburger button.

Desktop (>=900px) is untouched: the sidebar is the same markup, CSS
alone hides it below 900px and shows it above, so nothing there
changed behaviourally.

Claude-Session: https://claude.ai/code/session_01RHPj4ggeFdEjKKfm4SHbD7

internal/web/static/js/ui.js

@@ -34,6 +34,10 @@ export function clear(el, ...children) {
 const ICONS = {
   back: ['M15 18l-6-6 6-6'],
   more: ['M5 12h.01M12 12h.01M19 12h.01'],
+  queueList: ['M4 6h16M4 12h16M4 18h10'],
+  calendar: ['rect:3.5,5,17,15,2', 'M3.5 10h17M8 3v4M16 3v4'],
+  team: ['circle:9,8,3', 'circle:17,9,2.5', 'M3 19a6 6 0 0 1 12 0M15 19a5 5 0 0 1 6-4'],
+  shield: ['M12 3l7 3v6c0 4-3 7-7 9-4-2-7-5-7-9V6z'],
   check: ['M5 12.5l4.5 4.5L19 7'],
   checkCircle: ['M8 12.5l3 3 5-6', 'circle:12,12,9'],
   undo: ['M9 14L4 9l5-5', 'M4 9h10a6 6 0 0 1 0 12h-3'],
@@ -64,6 +68,14 @@ export function icon(name, cls = 'icon') {
       node.setAttribute('cx', cx);
       node.setAttribute('cy', cy);
       node.setAttribute('r', r);
+    } else if (d.startsWith('rect:')) {
+      const [x, y, w, hgt, rx] = d.slice(5).split(',');
+      node = document.createElementNS(SVG, 'rect');
+      node.setAttribute('x', x);
+      node.setAttribute('y', y);
+      node.setAttribute('width', w);
+      node.setAttribute('height', hgt);
+      if (rx) node.setAttribute('rx', rx);
     } else {
       node = document.createElementNS(SVG, 'path');
       node.setAttribute('d', d);