Let the account holder edit their own profile details

The Profile block is headed "Your profile", but the one person on it you
could not change was yourself: your name, your birth year, and whether you
take lessons yourself were fixed at whatever signup recorded, and correcting
any of them meant asking a studio admin.

A "Your details" section now opens the page, saved through the same
nonce-checked template_redirect post/redirect/get path the child rows use:

- Your name, written to display_name and nickname together, for the reason
  updateChild() does — UserName reads the nickname first, and leaving it
  behind would put the account's email address back on every screen that
  names a person.
- "I take lessons myself", the positive of us_guardian_only. This makes good
  on the claim already in bookableStudents() and the feature doc that a
  guardian-only account can put itself right from the profile page.
- Your birth year, held to the same normaliseBirthYear() rule as every other
  student.

The email is shown but not editable: it is the account's user_login as well
as its address, so changing it stays a studio-side job.

The birth-year field deliberately carries no `required` attribute. It is
asked of a student only, and this page loads no JavaScript, so a
browser-enforced `required` would leave a guardian who books solely for
other people unable to submit the form at all; handleSelf() enforces it
against the checkbox instead. Unticking the box does not clear a stored
birth year — it says who books, not "forget what is on file".

Closes #165

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

templates/frontend/family-page.php

@@ -8,6 +8,7 @@ if (! defined('ABSPATH')) {
 }
 
 /**
+ * @var array{name: string, email: string, birth_year: string, is_student: bool} $self The account holder's own details.
  * @var list<array{id: int, name: string, birth_year: string, relationship: string}> $children
  * @var list<\Unsupervised\Schedular\Registration\Question> $questions Account-scope questions, asked once per child.
  * @var string $error  Validation error from the last submission, if any.
@@ -26,6 +27,52 @@ if (! defined('ABSPATH')) {
         <p class="us-error" role="alert"><?php echo esc_html($error); ?></p>
     <?php endif; ?>
 
+    <form method="post" action="" class="us-family-self">
+        <?php wp_nonce_field('us_family'); ?>
+        <input type="hidden" name="us_family_action" value="self">
+
+        <h4><?php esc_html_e('Your details', 'unsupervised-schedular'); ?></h4>
+
+        <?php if ($self['email'] !== '') : ?>
+            <?php /* Shown, not editable: the address is the account's login, and changing it is a studio-side job. */ ?>
+            <p class="us-family-self-email">
+                <?php esc_html_e('Email', 'unsupervised-schedular'); ?>
+                <span><?php echo esc_html($self['email']); ?></span>
+            </p>
+        <?php endif; ?>
+
+        <p>
+            <label for="us-own-name"><?php esc_html_e('Your name', 'unsupervised-schedular'); ?> <span class="us-required" aria-hidden="true">*</span></label>
+            <input type="text" name="own_name" id="us-own-name" autocomplete="name" required value="<?php echo esc_attr($self['name']); ?>">
+        </p>
+        <p>
+            <label>
+                <input type="checkbox" name="is_student" value="1"<?php checked($self['is_student']); ?>>
+                <?php esc_html_e('I take lessons myself', 'unsupervised-schedular'); ?>
+            </label>
+            <span class="us-field-hint"><?php esc_html_e('Leave this unticked if you only book for the students below — you will not be offered as a student yourself.', 'unsupervised-schedular'); ?></span>
+        </p>
+        <?php
+        /*
+         * Asked of a student only, so `required` is deliberately absent: the box
+         * above is what decides, and the browser cannot be told to enforce a
+         * field conditionally without JavaScript this page does not load.
+         * `handleSelf()` enforces it on the server either way.
+         */
+        ?>
+        <p>
+            <label for="us-own-birth-year"><?php esc_html_e('Your birth year', 'unsupervised-schedular'); ?></label>
+            <input type="number" name="own_birth_year" id="us-own-birth-year" value="<?php echo esc_attr($self['birth_year']); ?>" min="1900" max="<?php echo esc_attr(current_time('Y')); ?>" step="1" inputmode="numeric" autocomplete="bday-year" placeholder="<?php esc_attr_e('YYYY', 'unsupervised-schedular'); ?>" aria-describedby="us-own-birth-year-hint">
+            <span class="us-field-hint" id="us-own-birth-year-hint"><?php esc_html_e('Needed only if you take lessons yourself.', 'unsupervised-schedular'); ?></span>
+        </p>
+
+        <p>
+            <button type="submit"><?php esc_html_e('Save my details', 'unsupervised-schedular'); ?></button>
+        </p>
+    </form>
+
+    <h4><?php esc_html_e('Your students', 'unsupervised-schedular'); ?></h4>
+
     <?php if (empty($children)) : ?>
         <p><?php esc_html_e('You have not added any students yet. Add one below to start booking lessons for them.', 'unsupervised-schedular'); ?></p>
     <?php else : ?>