Add studio-defined account-registration questions

Studio admins can now define registration questions that every new student
answers as a required second step during signup, with each student's answers
shown under a "Registration Information" section in the admin.

Extends the existing Registration domain: us_questions gains a scope column
(offering | account) and a nullable offering_id, and account answers reuse
us_question_answers with registration_type = 'account'. Authoring reuses the
Offerings -> Questions page via an "Account signup" scope (studio-admin only).
The registration form becomes two steps (progressive enhancement via
assets/js/register.js; works without JS); required answers are validated before
the account is created and apply to all signup paths (invite, group link,
self-approval). StudentHistory::registrationInfo() powers the admin section.

Bumps the plugin version to 1.1.0 so dbDelta runs the schema migration.

Closes #90

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/Schema.php

@@ -75,7 +75,8 @@ class Schema {
 
 			"CREATE TABLE {$prefix}us_questions (
                 id          BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
-                offering_id BIGINT UNSIGNED NOT NULL,
+                offering_id BIGINT UNSIGNED DEFAULT NULL,
+                scope       VARCHAR(20)     NOT NULL DEFAULT 'offering',
                 label       VARCHAR(255)    NOT NULL,
                 field_type  VARCHAR(20)     NOT NULL DEFAULT 'text',
                 options     TEXT,
@@ -85,6 +86,7 @@ class Schema {
                 created_at  DATETIME        NOT NULL,
                 PRIMARY KEY (id),
                 KEY offering_id (offering_id),
+                KEY scope (scope),
                 KEY is_active (is_active)
             ) {$charset};",