Add WebDAV support via Apache mod_dav

Backend:
- WebDAV config managed at /etc/apache2/conf-available/micronas-webdav.conf
  with BEGIN/END markers per share; reload apache2 on every write
- htpasswd file at /etc/micronas-webdav.passwd synced automatically on
  create_user, change_password, delete_user
- Full CRUD: POST/PATCH/DELETE /api/share/webdav[/<name>]
- _validate_webdav_users(): space-separated, no @group (not supported by Apache)
- Fix: _validate_users() now allows @groupname for SMB (was incorrectly rejected)
- Dashboard: apache2 status + restart button; webdav shares in /api/dashboard

Frontend:
- WebDAV tab: create form + table with clickable access URLs
- Edit modal supports 'webdav' type (name, path, users, permissions section)
- badge-webdav CSS class (green tint) in app.css
- dashboard.js renders badge-<type> dynamically (smb/nfs/webdav)

Docs: README WebDAV mount guide (Linux davfs2, Windows, Mac), PLANNING phase 4

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

static/js/dashboard.js

@@ -13,8 +13,9 @@ async function loadDashboard() {
         document.getElementById(id).style.display = 'flex';
         document.getElementById(id).style.alignItems = 'center';
     }
-    setDaemon('statusSmbd', 'smbd', d.status.smbd);
-    setDaemon('statusNfsd', 'nfsd', d.status.nfsd);
+    setDaemon('statusSmbd',    'smbd',    d.status.smbd);
+    setDaemon('statusNfsd',    'nfsd',    d.status.nfsd);
+    setDaemon('statusApache2', 'apache2', d.status.apache2);
 
     // Disk bar
     if (d.disk && !d.disk.error) {
@@ -43,7 +44,7 @@ async function loadDashboard() {
     } else {
         sb.innerHTML = d.shares.map(s => `
             <tr>
-                <td><span class="badge rounded-pill ${s.type === 'smb' ? 'badge-smb' : 'badge-nfs'}">${s.type.toUpperCase()}</span></td>
+                <td><span class="badge rounded-pill badge-${s.type}">${s.type.toUpperCase()}</span></td>
                 <td>${esc(s.name ?? '—')}</td>
                 <td><code>${esc(s.path)}</code></td>
                 <td style="color:var(--muted); font-size:.87em">${esc(s.access || '—')}</td>