Show price cadence and require a pay agreement at booking

Every price a student meets on the front end now carries the cadence it is
billed on — at booking, up front, weekly, monthly — so a bare amount can no
longer read as a one-off when it is a recurring charge.

Both registration forms then restate the price and require a second, separate
tick agreeing to pay it, distinct from the policy acceptances above it. The
agreed figure includes the studio HST so it matches Payment::total(), the amount
actually billed; the rate reaches the browser as a new localized `taxRate`.

A weekly reservation is charged per lesson for every week it claims, and a week
another student takes first is simply not claimed, so its total is quoted as a
ceiling ("up to 12 lessons") rather than a promise. Free offerings have nothing
to agree to and show no price block at all.

The formatting and the agreement live in one shared helper (`window.usPricing`,
registered as `us-scheduler-pricing`) so a price reads the same in the booking
form, the class catalogue and the editor preview.

Closes #124

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

assets/js/group-classes.js

@@ -152,7 +152,7 @@
                 ${o.instructor_name ? `<p class="us-class-instructor">With ${escHtml(o.instructor_name)}</p>` : ''}
                 ${o.schedule_note ? `<p>${escHtml(o.schedule_note)}</p>` : ''}
                 ${!singleOfferingId && o.description ? `<p>${escHtml(o.description)}</p>` : ''}
-                <p>${escHtml(Number(o.price).toFixed(2))} ${escHtml(o.currency)}</p>
+                <p class="us-class-price">${escHtml(window.usPricing.priceLabel(o))}</p>
                 ${!enrolledMap.has(Number(o.id)) && isEnrollmentOpen(o) && enrolmentDeadline(o)
         ? `<p class="us-enrol-deadline">Enrol by ${escHtml(formatDate(enrolmentDeadline(o)))}</p>`
         : ''}
@@ -204,6 +204,7 @@
                 <form id="us-enrol-form">
                     ${questions.map(questionField).join('')}
                     ${policies.map(policyField).join('')}
+                    ${window.usPricing.summaryHtml(offering)}
                     <p>
                         <button type="submit" class="us-enrol-btn">Confirm Enrolment</button>
                         <button type="button" id="us-group-cancel" class="us-cancel-btn">Back</button>
@@ -214,6 +215,10 @@
         document.getElementById('us-group-cancel').addEventListener('click', loadClasses);
         document.getElementById('us-enrol-form').addEventListener('submit', (e) => {
             e.preventDefault();
+            if (!window.usPricing.agreed(e.target)) {
+                showError(window.usPricing.AGREE_REQUIRED);
+                return;
+            }
             submitEnrolment(e.target, offering, questions);
         });
     }