Add field help dialog with cultivar/process reference notes

Adds a help-dialog UI (field-help.js/field-help-content.js) surfacing
per-field guidance, expands cultivar and process reference data with
cup notes, sweet-spot width, and watch-fors, and adds a Makefile for
common npm tasks.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

public/index.html

@@ -348,6 +348,24 @@
       </div>
     </aside>
 
+    <dialog class="help-dialog" id="field-help-dialog" aria-labelledby="help-dialog-title">
+      <div class="help-card">
+        <div class="help-head">
+          <div>
+            <span class="help-kicker">Field guide</span>
+            <h3 id="help-dialog-title"></h3>
+          </div>
+          <button class="icon-btn" type="button" data-close-help aria-label="Close">✕</button>
+        </div>
+        <div class="help-body" id="help-dialog-body"></div>
+        <p class="help-attrib">
+          Timing framework: Rob Hoos, <em>Cultivars: A Practical Guide for Coffee Roasters</em>.
+          Temperatures, bands and machine settings: your own logged roasts on the Hottop
+          KN-8828B-2K+ — they transfer to no other machine.
+        </p>
+      </div>
+    </dialog>
+
     <form id="plan-form">
       <div class="workspace-grid">
         <div class="form-col">