B1.3: isStable real threshold (config-driven, replaces tautology)

The legacy stdDev < stdDev*2 was always true. New behaviour: stdDev <=
config.calibration.stabilityThreshold OR stdDev === 0. Default
threshold 0.01 in scaling-units. Schema field + editor UI added. 4
BUG-PRESERVED tests rewritten + 4 new edge tests. 101/101 pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

measurement.html

@@ -34,6 +34,7 @@
       simulator: { value: false },
       smooth_method: { value: "" },
       count: { value: "10", required: true },
+      stabilityThreshold: { value: 0.01 },
       processOutputFormat: { value: "process" },
       dbaseOutputFormat: { value: "influxdb" },
 
@@ -227,6 +228,12 @@
         (field) => (node[field] = parseFloat(document.getElementById(`node-input-${field}`).value) || 0)
       );
 
+      // Calibration stability threshold: 0 is a valid (very strict) value, so
+      // fall back to the default 0.01 only when the field is empty / NaN.
+      const stRaw = document.getElementById('node-input-stabilityThreshold').value;
+      const stParsed = parseFloat(stRaw);
+      node.stabilityThreshold = Number.isFinite(stParsed) ? stParsed : 0.01;
+
       // Mode-dependent validation. In digital mode we don't care about
       // scaling completeness (the channels have their own per-channel
       // scaling); in analog mode we still warn about half-filled ranges.
@@ -329,6 +336,14 @@
       <input type="number" id="node-input-count" placeholder="10" style="width:60px;"/>
       <div class="form-tips">Number of samples for smoothing</div>
     </div>
+
+    <!-- Calibration Stability Threshold -->
+    <div class="form-row">
+      <label for="node-input-stabilityThreshold"><i class="fa fa-balance-scale"></i> Stability Threshold</label>
+      <input type="number" id="node-input-stabilityThreshold" placeholder="0.01" step="any" style="width:100px;"/>
+      <span style="margin-left:6px; color:#666;">(scaling-units)</span>
+      <div class="form-tips">Maximum stdDev of the rolling window for calibrate() and evaluateRepeatability() to accept the buffer as stable. Default 0.01.</div>
+    </div>
   </div>
 
   <hr>