webui: add pure calibration module with unit tests

Implements Calib JS module (calibration.js) with affine transform primitives,
CalTable, and normaliseCal matching Go CalConfig.Normalise semantics; 14 node
--test cases all pass. Loads before app.js in index.html.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Client/udpstreamer/static/index.html

@@ -216,6 +216,7 @@
     </div>
     <!-- Follows the mouse over a plot: time + per-trace values. -->
     <div id="hover-readout" style="display:none"></div>
+    <script src="/calibration.js"></script>
     <script src="/app.js"></script>
   </body>
 </html>