Let a studio pick its default payment method and disconnect Stripe

Stripe configuration was a one-way door. Keys could be entered but never
removed, and entering them moved every student onto card billing at once,
so there was no way to have Stripe live and satisfy yourself that card
payments worked before committing the studio to them.

Two settings-page changes open both directions:

Default payment method (`us_default_payment_method`) is now an explicit
choice between card and e-transfer for students with no per-student
override, rather than something inferred from whether keys exist. Card
remains the default, so a site that adds keys and changes nothing else
behaves as before. BillingMethodResolver still degrades a card default to
e-transfer while Stripe is unconfigured — there is nothing to charge a
card with — and `comp` is deliberately not offerable studio-wide, since
it would silently stop billing everybody; an unrecognised stored value
reads back as card. Holding the default on e-transfer with Stripe live is
the staged-rollout path: move individual students to card on their detail
page, watch real charges land, then flip the studio over.

Clear Stripe configuration deletes the publishable key, secret key and
webhook signing secret and returns the mode to test, so a re-configuration
later cannot inherit live. Currency, HST, e-transfer and registration
settings are untouched, as are recorded payments. The button only appears
when some Stripe value is stored, and reuses the page's existing nonce and
`manage_billing` check.

`composer test` (915), `composer lint` and `composer cs` all pass. Options
only — no schema change, so no version bump.

Closes #173

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01WyktWmwNRgMYuwe5eBuPZm

templates/admin/settings.php

@@ -15,6 +15,9 @@ if (! defined('ABSPATH')) {
  * @var string $etransferEmail
  * @var float  $hstRate
  * @var bool   $stripeConfigured
+ * @var string $defaultMethod
+ * @var bool   $stripeAnySet
+ * @var string $notice
  * @var bool   $openRegistration
  * @var int    $cancellationCutoffDays
  */
@@ -22,10 +25,18 @@ if (! defined('ABSPATH')) {
 <div class="wrap">
     <h1><?php esc_html_e('Studio Settings', 'unsupervised-schedular'); ?></h1>
 
+    <?php if ('' !== $notice) : ?>
+        <div class="notice notice-success inline">
+            <p><?php echo esc_html($notice); ?></p>
+        </div>
+    <?php endif; ?>
+
     <div class="notice notice-info inline">
         <p>
-            <?php if ($stripeConfigured) : ?>
+            <?php if ($stripeConfigured && 'card' === $defaultMethod) : ?>
                 <?php esc_html_e('Stripe is configured — new registrations default to credit-card billing.', 'unsupervised-schedular'); ?>
+            <?php elseif ($stripeConfigured) : ?>
+                <?php esc_html_e('Stripe is configured, but the studio default is e-transfer — only students you switch to credit card individually are billed by card.', 'unsupervised-schedular'); ?>
             <?php else : ?>
                 <?php esc_html_e('Stripe is not configured — new registrations default to e-transfer, which a studio admin marks paid on receipt. Add your Stripe keys below to enable card billing.', 'unsupervised-schedular'); ?>
             <?php endif; ?>
@@ -80,6 +91,31 @@ if (! defined('ABSPATH')) {
             </tr>
         </table>
 
+        <h2><?php esc_html_e('Billing', 'unsupervised-schedular'); ?></h2>
+        <table class="form-table">
+            <tr>
+                <th scope="row"><?php esc_html_e('Default payment method', 'unsupervised-schedular'); ?></th>
+                <td>
+                    <fieldset>
+                        <label>
+                            <input type="radio" name="default_payment_method" value="card" <?php checked($defaultMethod, 'card'); ?>>
+                            <?php esc_html_e('Credit card (requires Stripe)', 'unsupervised-schedular'); ?>
+                        </label><br>
+                        <label>
+                            <input type="radio" name="default_payment_method" value="etransfer" <?php checked($defaultMethod, 'etransfer'); ?>>
+                            <?php esc_html_e('E-transfer', 'unsupervised-schedular'); ?>
+                        </label>
+                        <p class="description">
+                            <?php esc_html_e('Applies to every student without their own billing method. Keep this on e-transfer while you trial card payments: switch individual students to Credit card under Students → student detail → Billing method, confirm their bookings charge correctly, then move the whole studio over by changing this setting.', 'unsupervised-schedular'); ?>
+                        </p>
+                        <?php if (! $stripeConfigured) : ?>
+                            <p class="description"><?php esc_html_e('Credit card has no effect until Stripe keys are saved above — until then every student is billed by e-transfer.', 'unsupervised-schedular'); ?></p>
+                        <?php endif; ?>
+                    </fieldset>
+                </td>
+            </tr>
+        </table>
+
         <h2><?php esc_html_e('E-transfer', 'unsupervised-schedular'); ?></h2>
         <table class="form-table">
             <tr>
@@ -124,4 +160,16 @@ if (! defined('ABSPATH')) {
         </table>
         <?php submit_button(esc_html__('Save Settings', 'unsupervised-schedular')); ?>
     </form>
+
+    <?php if ($stripeAnySet) : ?>
+        <h2><?php esc_html_e('Clear Stripe configuration', 'unsupervised-schedular'); ?></h2>
+        <p class="description">
+            <?php esc_html_e('Forgets the publishable key, secret key and webhook signing secret, and returns the mode to Test. Billing falls back to e-transfer until Stripe is set up again; payments already recorded are untouched.', 'unsupervised-schedular'); ?>
+        </p>
+        <form method="post" onsubmit="return confirm('<?php echo esc_js(esc_html__('Clear the stored Stripe keys? Card billing stops until you enter them again.', 'unsupervised-schedular')); ?>');">
+            <?php wp_nonce_field('usc_settings_action'); ?>
+            <input type="hidden" name="usc_action" value="clear_stripe">
+            <?php submit_button(esc_html__('Clear Stripe configuration', 'unsupervised-schedular'), 'delete', 'submit', true); ?>
+        </form>
+    <?php endif; ?>
 </div>