Require a name and birth year for every student

Both fields are marked in their labels the same way a required registration
question is, and enforced on the server whichever form they arrive from:
GuardianService::createChild() and updateChild() now refuse a blank name or
an unusable birth year, and the signup form checks the same rule up front,
before it creates a single user, so a bad block never leaves a
half-registered family behind. normaliseBirthYear() became public and static
so both paths share one definition of what a usable year is.

The signup form cannot lean on the browser here. Its child blocks are hidden
until the parent/guardian box is ticked, and a `required` field inside a
hidden container makes the whole form unsubmittable with no control the user
can reach to fix — the same trap the guardian's own question panel already
sidesteps by disabling rather than hiding. So register.js puts `required` on
and takes it off along with the block itself, and the server is what makes
the rule hold with JavaScript off. The profile screen has no such problem:
its forms are always visible, so the attribute is static there.

One behaviour change beyond the requirement: a child block with anything
typed into it is now reported back instead of dropped. Previously any block
without a name was silently discarded, which would now mean losing a birth
year the guardian had filled in. A wholly untouched spare block — the one
the form always renders for "add another" — is still ignored.

Verified the required-toggling in a headless browser: unticked submits,
ticked blocks an empty block, a cloned block inherits the requirement, and
re-unticking leaves nothing behind to block a non-guardian signup.

Closes #148

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

tests/Unit/Guardian/GuardianServiceTest.php

@@ -116,20 +116,35 @@ class GuardianServiceTest extends TestCase
 
         Functions\expect('wp_delete_user')->once()->with(42);
 
-        self::assertInstanceOf(\WP_Error::class, $this->service->createChild(5, 'Ada'));
+        self::assertInstanceOf(\WP_Error::class, $this->service->createChild(5, 'Ada', '2015'));
     }
 
     /**
      * @dataProvider unusableBirthYears
      */
-    public function testCreateChildClearsAnUnusableBirthYear(string $submitted): void
+    public function testCreateChildRefusesAnUnusableBirthYear(string $submitted): void
     {
-        Functions\when('wp_insert_user')->justReturn(42);
-        $this->guardians->shouldReceive('insert')->once()->andReturn(7);
+        // Refused before anything is written, so no orphan user is left behind.
+        Functions\expect('wp_insert_user')->never();
+        $this->guardians->shouldNotReceive('insert');
 
-        $this->service->createChild(5, 'Ada', $submitted);
+        $result = $this->service->createChild(5, 'Ada', $submitted);
 
-        self::assertArrayNotHasKey(GuardianService::META_BIRTH_YEAR, $this->meta[42] ?? []);
+        self::assertInstanceOf(\WP_Error::class, $result);
+        self::assertSame('missing_birth_year', $result->get_error_code());
+        self::assertArrayNotHasKey(42, $this->meta);
+    }
+
+    /** @dataProvider unusableBirthYears */
+    public function testUpdateChildRefusesAnUnusableBirthYear(string $submitted): void
+    {
+        $this->guardians->shouldReceive('isGuardianOf')->with(5, 42)->andReturn(true);
+        Functions\expect('wp_update_user')->never();
+
+        $result = $this->service->updateChild(5, 42, 'Ada', $submitted);
+
+        self::assertInstanceOf(\WP_Error::class, $result);
+        self::assertSame('missing_birth_year', $result->get_error_code());
     }
 
     /** @return array<string, array{string}> */
@@ -142,6 +157,7 @@ class GuardianServiceTest extends TestCase
             'too many digits'   => ['20155'],
             'before 1900'       => ['1899'],
             'later than today'  => ['2027'],
+            'left blank'        => [''],
         ];
     }
 
@@ -230,9 +246,8 @@ class GuardianServiceTest extends TestCase
     }
 
     /**
-     * Saving a child drops the legacy full date. Without that, clearing the birth
-     * year on a child who predates the change would leave the old date behind for
-     * the fallback above to resurrect on the next read.
+     * Saving a child drops the legacy full date, so the fallback above can never
+     * outrank a year the guardian has since corrected by hand.
      */
     public function testSavingAChildClearsTheLegacyDateOfBirth(): void
     {
@@ -241,15 +256,16 @@ class GuardianServiceTest extends TestCase
         $this->guardians->shouldReceive('isGuardianOf')->with(5, 42)->andReturn(true);
         Functions\when('wp_update_user')->justReturn(42);
 
-        self::assertNull($this->service->updateChild(5, 42, 'Ada L', ''));
+        self::assertNull($this->service->updateChild(5, 42, 'Ada L', '2016'));
 
         self::assertArrayNotHasKey(GuardianService::META_DOB, $this->meta[42] ?? []);
-        self::assertArrayNotHasKey(GuardianService::META_BIRTH_YEAR, $this->meta[42] ?? []);
+        self::assertSame('2016', $this->meta[42][GuardianService::META_BIRTH_YEAR]);
 
+        // The corrected year is what is read back, not the year of the old date.
         $this->guardians->shouldReceive('findByGuardian')->with(5)->andReturn([new GuardianLink(5, 42)]);
         Functions\when('get_userdata')->justReturn($this->user(42, 'Ada', 'Lovelace'));
 
-        self::assertSame('', $this->service->children(5)[0]['birth_year']);
+        self::assertSame('2016', $this->service->children(5)[0]['birth_year']);
     }
 
     public function testBookableStudentsIsJustTheUserWithoutChildren(): void