Add mobile responsiveness + PWA support

Mobile (768px):
- Tab bar: horizontal scroll with momentum, hidden scrollbar
- Header: compact layout, smaller fonts
- Tables: horizontal scroll, hide-mobile class for less important cols
- Modals: bottom-sheet style, full width
- Touch targets: min-height 36px for buttons/selects
- Toolbar: stacks vertically
- Stat cards: compact

Small phone (480px):
- Even more compact header and tabs
- Smaller table cells
- iOS zoom prevention (16px font on inputs)

PWA:
- manifest.json for Add to Home Screen
- apple-mobile-web-app-capable meta tags
- theme-color for status bar
- overscroll-behavior: none (prevent pull-to-refresh)

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

script.js

@@ -1208,9 +1208,9 @@ function renderUserRow(u, companyId) {
     return `<tr>
         <td><strong>${esc(u.username)}</strong></td>
         <td>${esc(u.nimi)}</td>
-        <td>${esc(u.email || '')}</td>
+        <td class="hide-mobile">${esc(u.email || '')}</td>
         <td>${role}</td>
-        <td>${esc(u.luotu)}</td>
+        <td class="hide-mobile">${esc(u.luotu)}</td>
         <td class="actions-cell">
             <button onclick="editUser('${u.id}')" title="Muokkaa">&#9998;</button>
             ${u.id !== currentUser?.id ? `<button onclick="deleteUser('${u.id}','${esc(u.username)}')" title="Poista">&#128465;</button>` : ''}