feat(measure): memorizza tempo di inserimento misura (input_duration_ms)

Colonna nullable su measurements + migration 003, campo opzionale negli
schemi API (create singola e batch), passthrough nel proxy Flask e timer
lato client in task_execute: parte all'attivazione del subtask, si
resetta su auto-advance e navigazione manuale.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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

@@ -729,6 +729,9 @@ function taskExecute() {
     // ---- Value from numpad / caliper ----
     currentValue: null,
 
+    // ---- Input timing (ms spent on the active subtask) ----
+    inputStartedAt: null,
+
     // ---- Image switching logic ----
     get currentSubtaskImage() {
       return this.currentSubtask?.image_path || null;
@@ -808,6 +811,7 @@ function taskExecute() {
     // ---- Init ----
     init() {
       this.subtasks.sort((a, b) => (a.order_index || 0) - (b.order_index || 0));
+      this.inputStartedAt = Date.now();
     },
 
     // ---- Check if a subtask has been measured ----
@@ -834,6 +838,9 @@ function taskExecute() {
 
       const pf = this.passFailStatus;
       const dev = this.deviation;
+      const inputDurationMs = this.inputStartedAt !== null
+        ? Math.max(0, Math.round(Date.now() - this.inputStartedAt))
+        : null;
 
       this.saving = true;
 
@@ -853,6 +860,7 @@ function taskExecute() {
             lot_number: this.lotNumber,
             serial_number: this.serialNumber,
             input_method: inputMethod || 'manual',
+            input_duration_ms: inputDurationMs,
           }),
         });
 
@@ -911,6 +919,7 @@ function taskExecute() {
     // ---- Advance to next unmeasured subtask ----
     advanceToNext() {
       this.currentValue = null;
+      this.inputStartedAt = Date.now();
 
       for (let i = this.currentIndex + 1; i < this.totalSubtasks; i++) {
         if (!this.isMeasured(this.subtasks[i].id)) {
@@ -932,6 +941,7 @@ function taskExecute() {
         this.currentIndex = index;
         this.currentValue = null;
         this.errorMessage = '';
+        this.inputStartedAt = Date.now();
       }
     },