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]>

src/BlockPreview.php

@@ -176,10 +176,26 @@ class BlockPreview {
 	}
 
 	/**
-	 * Sample family (manage-children) page: two representative children and the
-	 * add form, with the controls inert so the editor preview cannot post.
+	 * Sample family page: the account holder's own details, two representative
+	 * children and the add form, with the controls inert so the editor preview
+	 * cannot post.
 	 */
 	public static function family(): string {
+		$self = sprintf(
+			'<h4>%s</h4><p class="us-family-self-email">%s <span>[email protected]</span></p>'
+				. '<p><label for="us-own-name">%s' . self::REQUIRED_MARK . '</label><input type="text" id="us-own-name" value="%s"></p>'
+				. '<p><label><input type="checkbox" checked disabled> %s</label></p>'
+				. '<p><label for="us-own-birth-year">%s</label><input type="number" id="us-own-birth-year" placeholder="YYYY"></p>'
+				. '<p><button type="button" disabled>%s</button></p>',
+			esc_html__( 'Your details', 'unsupervised-schedular' ),
+			esc_html__( 'Email', 'unsupervised-schedular' ),
+			esc_html__( 'Your name', 'unsupervised-schedular' ),
+			esc_attr__( 'Grace Hopper', 'unsupervised-schedular' ),
+			esc_html__( 'I take lessons myself', 'unsupervised-schedular' ),
+			esc_html__( 'Your birth year', 'unsupervised-schedular' ),
+			esc_html__( 'Save my details', 'unsupervised-schedular' )
+		);
+
 		$children = '';
 		foreach ( [ 'Ada Lovelace', 'Alan Turing' ] as $name ) {
 			$children .= sprintf(
@@ -202,9 +218,12 @@ class BlockPreview {
 		);
 
 		return sprintf(
-			'<div class="us-family">%s<h3>%s</h3><ul class="us-family-list">%s</ul><form class="us-family-add">%s</form></div>',
-			self::note( __( 'Editor preview — signed-in guardians see and manage their own students here.', 'unsupervised-schedular' ) ),
+			'<div class="us-family">%s<h3>%s</h3><form class="us-family-self">%s</form>'
+				. '<h4>%s</h4><ul class="us-family-list">%s</ul><form class="us-family-add">%s</form></div>',
+			self::note( __( 'Editor preview — signed-in visitors see and manage their own details and students here.', 'unsupervised-schedular' ) ),
 			esc_html__( 'Your profile', 'unsupervised-schedular' ),
+			$self,
+			esc_html__( 'Your students', 'unsupervised-schedular' ),
 			$children,
 			$add
 		);