Fix New plan feeling like a no-op; add plan delete and why-panel collapse

New plan reset the form correctly but left the Plans drawer open over
it, so the reset was invisible until the user closed the drawer
themselves. Now closes it immediately, matching selectPlan().

Also adds a delete button per plan in the Plans drawer (server route
already existed) - deleting the currently open plan resets to a fresh
blank one, matching New plan.

Why-panel teaching callouts ("WHY CULTIVAR SETS THE CLOCK" etc.) now
default collapsed instead of wall-to-wall expanded on first load, with
an "Expand all" button in the header on both the planner and cupping
pages. Persistence flips from tracking collapsed-vs-default-open to
expanded-vs-default-closed to match.

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

public/cupping.html

@@ -88,6 +88,9 @@
               ><span class="dot"></span
               ><span class="autosave-text">Not saved yet</span></span
             >
+            <button id="btn-expand-why" type="button" class="ghost-btn">
+              Expand all "why" notes
+            </button>
           </div>
         </header>
         <div class="drawer-overlay hidden" id="drawer-overlay"></div>
@@ -160,7 +163,7 @@
                   </label>
                 </div>
                 <div class="panel-body">
-                  <details class="why-panel" data-why="cup-scores" open>
+                  <details class="why-panel" data-why="cup-scores">
                     <summary>Why the scale starts at 6</summary>
                     <p>
                       The 6–10 range is a specialty-grading convention:
@@ -186,7 +189,7 @@
               <section class="panel-card" id="cup-flavors">
                 <div class="panel-head"><h2>Flavors</h2></div>
                 <div class="panel-body">
-                  <details class="why-panel" data-why="cup-flavors" open>
+                  <details class="why-panel" data-why="cup-flavors">
                     <summary>Tag what you can point at</summary>
                     <p>
                       A tag is only useful if you could defend it to
@@ -206,7 +209,7 @@
               <section class="panel-card" id="cup-notes">
                 <div class="panel-head"><h2>Notes</h2></div>
                 <div class="panel-body">
-                  <details class="why-panel" data-why="cup-notes" open>
+                  <details class="why-panel" data-why="cup-notes">
                     <summary>Notes outlive scores</summary>
                     <p>
                       Numbers compare roasts; sentences explain them. Write