feat: sync DB prefs, update history tab, configurable dashboard shortcuts

- auth store fetchMe(): sync theme/sidebar_position/lang from DB to localStorage+stores on login/refresh
- profilePage setters: PATCH /api/auth/preferences on every preference change
- updatesPage: add history tab (GET /api/updates/history) with job list, click to view output
- dashboardPage: load shortcuts from settings API, fall back to defaults if none configured
- settingsPage: new Raccourcis tab to add/remove/configure dashboard shortcuts (saved as JSON)
- settings.go: expose dashboard_shortcuts in publicSettings for GET/PUT access
- pages.css: add .history-table, .shortcut-row styles

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

frontend/dashboard.html

@@ -140,15 +140,12 @@
               <div class="widget-links">
                 <h4 class="widget-title" x-text="t('dashboard.widgetShortcut')"></h4>
                 <div class="links-grid">
-                  <a class="neu-btn link-btn" href="/proxmox.html" @click.prevent="navigate('/proxmox.html')">
-                    <i class="lnid-server-1"></i> Proxmox
-                  </a>
-                  <a class="neu-btn link-btn" href="/terminal.html" @click.prevent="navigate('/terminal.html')">
-                    <i class="lnid-terminal"></i> Terminal
-                  </a>
-                  <a class="neu-btn link-btn" href="/updates.html" @click.prevent="navigate('/updates.html')">
-                    <i class="lnid-arrow-upward"></i> Updates
-                  </a>
+                  <template x-for="s in displayShortcuts" :key="s.href">
+                    <a class="neu-btn link-btn" :href="s.href" @click.prevent="navigate(s.href)">
+                      <i :class="s.icon"></i>
+                      <span x-text="s.label"></span>
+                    </a>
+                  </template>
                 </div>
               </div>
             </template>