Add multi-use group invite links with expiry and auto-approval on email confirmation

A studio admin can generate a shareable group invite link (e.g. for a
newsletter) from the Invites page, choosing a required expiry date. Anyone
with the link may register while it is valid, in any registration mode: the
form collects their own email, they must confirm it via the usual hashed
token, and confirming approves the account immediately — group signups never
enter the Pending Students queue.

- us_invites grows kind (personal/group) and expires_at; an explicit expiry
  wins over the personal 14-day window. Group links stay pending (multi-use)
  until revoked or expired.
- RegistrationPage: group signups create the account pending with the
  us_auto_approve marker and send the confirmation email; no auto-login.
- EmailConfirmationHandler: auto-approve accounts are approved on
  confirmation, emailed the approved notice, and redirected to a new
  us_confirmed=ready notice with a sign-in link.

Closes #77

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

src/Auth/Invite.php

@@ -11,6 +11,12 @@ class Invite {
 	public const STATUS_ACCEPTED = 'accepted';
 	public const STATUS_REVOKED  = 'revoked';
 
+	/** Single-use invite addressed to one email. */
+	public const KIND_PERSONAL = 'personal';
+
+	/** Multi-use shareable link (e.g. for a newsletter) with an explicit expiry. */
+	public const KIND_GROUP = 'group';
+
 	/**
 	 * All valid invite statuses.
 	 *
@@ -43,6 +49,8 @@ class Invite {
 		public readonly ?int $acceptedUserId = null,
 		public readonly ?string $acceptedAt = null,
 		public readonly ?string $createdAt = null,
+		public readonly string $kind = self::KIND_PERSONAL,
+		public readonly ?string $expiresAt = null,
 		public readonly ?int $id = null,
 	) {}
 
@@ -56,27 +64,44 @@ class Invite {
 			acceptedUserId: Val::intOrNull( $row->accepted_user_id ),
 			acceptedAt:     Val::stringOrNull( $row->accepted_at ),
 			createdAt:      Val::stringOrNull( $row->created_at ?? null ),
+			kind:           '' !== Val::string( $row->kind ?? '' ) ? Val::string( $row->kind ) : self::KIND_PERSONAL,
+			expiresAt:      Val::stringOrNull( $row->expires_at ?? null ),
 			id:             Val::int( $row->id ),
 		);
 	}
 
+	public function isGroup(): bool {
+		return self::KIND_GROUP === $this->kind;
+	}
+
 	public function isPending(): bool {
 		return self::STATUS_PENDING === $this->status;
 	}
 
 	/**
-	 * Whether the invite was created more than {@see EXPIRY_DAYS} ago, measured
-	 * against the supplied current `Y-m-d H:i:s` timestamp. An invite with no
-	 * known creation time is treated as not expired.
+	 * Whether the invite has expired, measured against the supplied current
+	 * `Y-m-d H:i:s` timestamp. An explicit `expires_at` (set on every group
+	 * link) wins; otherwise a personal invite expires {@see EXPIRY_DAYS} after
+	 * creation. An invite with neither timestamp is treated as not expired.
 	 */
 	public function isExpired( string $now ): bool {
+		$current = strtotime( $now );
+		if ( false === $current ) {
+			return false;
+		}
+
+		if ( null !== $this->expiresAt ) {
+			$expires = strtotime( $this->expiresAt );
+
+			return false !== $expires && $current > $expires;
+		}
+
 		if ( null === $this->createdAt ) {
 			return false;
 		}
 
 		$created = strtotime( $this->createdAt );
-		$current = strtotime( $now );
-		if ( false === $created || false === $current ) {
+		if ( false === $created ) {
 			return false;
 		}
 
@@ -101,10 +126,12 @@ class Invite {
 			'email'            => $this->email,
 			'token'            => $this->token,
 			'role'             => $this->role,
+			'kind'             => $this->kind,
 			'status'           => $this->status,
 			'invited_by'       => $this->invitedBy,
 			'accepted_user_id' => $this->acceptedUserId,
 			'accepted_at'      => $this->acceptedAt,
+			'expires_at'       => $this->expiresAt,
 		];
 	}
 }