fix(measure): supervisor modal — backspace works and fields reset

Two issues with the "Autorizzazione capoturno" modal:

1. Backspace and digits did not work in the username/password fields. The
   numpad component installs a window-level keydown handler (for the USB
   caliper / keyboard wedge) that preventDefault()s digits, Backspace, Enter
   etc. It swallowed those keys inside the modal inputs. Guard handleKeydown
   to ignore events whose target is an editable field (INPUT/TEXTAREA/SELECT/
   contentEditable); the numpad has no text inputs of its own.

2. The modal kept the previous username/password: opening only set the flag,
   and closing via backdrop click did not clear the fields. Add
   openSupervisorModal()/closeSupervisorModal() that always reset username,
   password and error, and use them for every open (fermo_linea,
   fine_produzione, out_of_tolerance) and close (backdrop, Annulla).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/frontend/flask_app/static/js/numpad.js

@@ -163,6 +163,17 @@ function numpad() {
      * @param {KeyboardEvent} e - The keyboard event
      */
     handleKeydown(e) {
+      // Ignore keystrokes aimed at an editable field (e.g. the supervisor
+      // login modal). The numpad has no text inputs of its own, so this
+      // window-level capture is only meant for the USB caliper / keyboard
+      // wedge when no field is focused. Without this guard the numpad would
+      // swallow digits and Backspace inside those inputs.
+      const t = e.target;
+      if (t && (t.tagName === 'INPUT' || t.tagName === 'TEXTAREA' ||
+                t.tagName === 'SELECT' || t.isContentEditable)) {
+        return;
+      }
+
       // Number keys
       if (e.key >= '0' && e.key <= '9') {
         e.preventDefault();

src/frontend/flask_app/templates/measure/task_execute.html

@@ -116,14 +116,14 @@
       {# Fermo linea + Fine produzione (measurement tasks only) #}
       <template x-if="subtasks.length > 0">
         <div class="shrink-0 flex items-center gap-1.5">
-          <button @click="showSupervisorModal = true; supervisorAction = 'fermo_linea'"
+          <button @click="openSupervisorModal('fermo_linea')"
                   class="btn text-xs py-1 px-2.5 gap-1 border-2 border-amber-500 text-amber-700 dark:text-amber-300 bg-amber-50 dark:bg-amber-900/20 hover:bg-amber-100 dark:hover:bg-amber-900/40">
             <svg class="w-3.5 h-3.5" fill="none" stroke="currentColor" stroke-width="2" viewBox="0 0 24 24">
               <path stroke-linecap="round" stroke-linejoin="round" d="M10 9v6m4-6v6m7-3a9 9 0 11-18 0 9 9 0 0118 0z"/>
             </svg>
             {{ _('Fermo linea') }}
           </button>
-          <button @click="showSupervisorModal = true; supervisorAction = 'fine_produzione'"
+          <button @click="openSupervisorModal('fine_produzione')"
                   class="btn text-xs py-1 px-2.5 gap-1 border-2 border-red-500 text-red-700 dark:text-red-300 bg-red-50 dark:bg-red-900/20 hover:bg-red-100 dark:hover:bg-red-900/40">
             <svg class="w-3.5 h-3.5" fill="none" stroke="currentColor" stroke-width="2" viewBox="0 0 24 24">
               <path stroke-linecap="round" stroke-linejoin="round" d="M21 12a9 9 0 11-18 0 9 9 0 0118 0z"/>
@@ -607,7 +607,7 @@
        x-transition:leave-end="opacity-0"
        x-cloak
        class="fixed inset-0 z-[60] flex items-center justify-center bg-black/50 backdrop-blur-sm"
-       @click.self="showSupervisorModal = false">
+       @click.self="closeSupervisorModal()">
     <div class="bg-[var(--bg-card)] rounded-2xl shadow-2xl p-6 max-w-sm mx-4 w-full border border-[var(--border-color)]">
       <div class="flex items-center gap-3 mb-4">
         <div class="w-10 h-10 rounded-full bg-amber-100 dark:bg-amber-900/30 flex items-center justify-center">
@@ -636,7 +636,7 @@
       </div>
 
       <div class="flex gap-2">
-        <button @click="showSupervisorModal = false; supervisorUsername = ''; supervisorPassword = ''; supervisorError = ''"
+        <button @click="closeSupervisorModal()"
                 class="btn btn-secondary flex-1 text-sm">
           {{ _('Annulla') }}
         </button>
@@ -858,8 +858,7 @@ function taskExecute() {
         // Out-of-tolerance: block advancement, require supervisor
         if (pf === 'fail') {
           this.pendingAdvance = true;
-          this.supervisorAction = 'out_of_tolerance';
+          this.openSupervisorModal('out_of_tolerance');
-          this.showSupervisorModal = true;
           return;
         }
 
@@ -998,6 +997,22 @@ function taskExecute() {
       }
     },
 
+    // ---- Open/close supervisor modal (always reset fields) ----
+    openSupervisorModal(action) {
+      this.supervisorAction = action;
+      this.supervisorUsername = '';
+      this.supervisorPassword = '';
+      this.supervisorError = '';
+      this.showSupervisorModal = true;
+    },
+
+    closeSupervisorModal() {
+      this.showSupervisorModal = false;
+      this.supervisorUsername = '';
+      this.supervisorPassword = '';
+      this.supervisorError = '';
+    },
+
     // ---- Supervisor reason text ----
     get supervisorReason() {
       if (this.supervisorAction === 'out_of_tolerance') return '{{ _("Misurazione fuori tolleranza") }}';