Add configurable label font size; bump to 0.76

- New "Label size (mm)" field controlling the numeric-label font size,
  defaulting to a clean 9 mm (was the inherited Inkscape value 8.89194)
- Pin k8s deployment to image tag 0.76

web/templates/index.html

@@ -350,12 +350,16 @@
             <span style="font-family:var(--f-mono);font-size:0.65rem;color:var(--muted)">(Labels minus one) should divide evenly into Major intervals for best appearance</span>
           </div>
         </div>
-        <div class="row" style="margin-top:1.25rem">
+        <div class="row row-2" style="margin-top:1.25rem">
           <div class="field">
             <label>Custom labels (optional)</label>
             <input name="labels" type="text" placeholder="e.g. Lo, 25, Mid, 75, Hi — leave blank to use calculated values">
             <span style="font-family:var(--f-mono);font-size:0.65rem;color:var(--muted)">Comma-separated. When set, overrides the calculated numbers and its count sets the number of labels.</span>
           </div>
+          <div class="field">
+            <label>Label size (mm)</label>
+            <input name="label_size" type="number" step="any" min="0.5" max="25" value="9" required>
+          </div>
         </div>
       </div>