feat(central-ui): add Min time between runs field to the script form

The template script editor had no input for MinTimeBetweenRuns, so a
WhileTrue trigger configured through the UI always saved a null interval
and degraded to a single edge fire. The Add/Edit Script modal now has a
"Min time between runs" number+unit (ms/sec/min) field.

- Visible only for ValueChange / Conditional / Expression triggers — the
  auto-firing triggers MinTimeBetweenRuns throttles. Hidden for Interval
  (its own period is the cadence), Call (invoked explicitly, never
  throttled), and None.
- For a WhileTrue Conditional/Expression trigger the field is labelled as
  the re-fire interval and shows a warning while it is blank.
- Wired through the new-script and edit-script save paths (edit previously
  only preserved the existing value, never let the user change it).

New DurationInput helper does the TimeSpan <-> number+unit conversion;
ScriptTriggerConfigCodec.SupportsMinTimeBetweenRuns classifies trigger
types. Both TDD'd — 21 new tests. CentralUI suite 316 green; verified
end-to-end in the browser (visibility per trigger type, WhileTrue warning,
save/reload round-trip).

tests/ScadaLink.CentralUI.Tests/Shared/ScriptTriggerConfigCodecTests.cs

@@ -117,6 +117,27 @@ public class ScriptTriggerConfigCodecTests
         Assert.Equal(mode, reparsed.Mode);
     }
 
+    // ── SupportsMinTimeBetweenRuns ─────────────────────────────────────────
+
+    [Theory]
+    [InlineData("ValueChange")]
+    [InlineData("Conditional")]
+    [InlineData("Expression")]
+    public void SupportsMinTimeBetweenRuns_TrueForAutoTriggersThatThrottle(string triggerType)
+    {
+        Assert.True(ScriptTriggerConfigCodec.SupportsMinTimeBetweenRuns(triggerType));
+    }
+
+    [Theory]
+    [InlineData("Interval")]   // has its own period control
+    [InlineData("Call")]       // invoked explicitly — no throttle applies
+    [InlineData(null)]         // None — never runs automatically
+    [InlineData("Bogus")]      // Unknown trigger type
+    public void SupportsMinTimeBetweenRuns_FalseForIntervalCallNoneAndUnknown(string? triggerType)
+    {
+        Assert.False(ScriptTriggerConfigCodec.SupportsMinTimeBetweenRuns(triggerType));
+    }
+
     [Theory]
     [InlineData(false)]
     [InlineData(true)]