feat: build a ready capacity-fit Today plan (Closes #633)

frontend/index.html

@@ -254,6 +254,8 @@
     <label class="plan-today-available" for="plan-today-available">Available today
       <span><input id="plan-today-available" type="number" inputmode="numeric" min="15" max="1440" step="15" placeholder="Minutes" /> min</span>
     </label>
+    <button class="plan-today-build" id="build-today-plan" type="button">Build my Today</button>
+    <div class="small plan-today-build-status" id="plan-today-build-status" role="status" aria-live="polite"></div>
     <div class="small plan-today-error" id="plan-today-error" role="alert"></div>
     <button class="discard-recap-replan" id="discard-recap-replan" type="button" hidden>Discard recap feedback</button>
     <section aria-labelledby="today-plan-heading">