fix: CSS reset, settings API, modules champs, proxmox token

- CSS: ajout reset (box-sizing, margin, font-family, body background)
- Settings: save par PUT /api/settings/{key} (pas bulk), un appel par clé
- Settings: proxmox_token champ unique (format user@realm!id=secret)
- Modules: is_enabled/is_core (champs backend réels, pas enabled/core)
- Proxmox: supprime bouton reboot (route inexistante)

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

frontend/proxmox.html

@@ -86,10 +86,6 @@
                   @click="action(r.vmid,'lxc','stop')" :disabled="actionLoading[r.vmid+'-stop']">
                   ⏹ Stop
                 </button>
-                <button class="neu-btn neu-btn--sm" x-show="r.status==='running'"
-                  @click="action(r.vmid,'lxc','reboot')" :disabled="actionLoading[r.vmid+'-reboot']">
-                  ↺ Reboot
-                </button>
               </div>
             </div>
           </template>