Add Offerings domain and studio-admin capabilities

Implements the offerings catalog (#1): private-lesson types and group
classes carrying pricing, billing mode (one_time/full_term), duration,
capacity, and term details. Adds the src/Offering/ domain (value object,
repository, REST endpoint, admin controller + template), the us_offerings
table, and an Offerings admin page.

Also lands the capability slice of #9: registers the us_studio_admin role
and the new capability strings (manage_instructors, manage_offerings,
manage_questions, manage_policies, manage_billing, view_all_payments,
view_own_payments, export_payments) so offering management gates correctly.

Tests: tests/Unit/Offering/ (value object + repository) and a studio-admin
case in RoleManagerTest. composer test, cs, and PHPStan level 6 all pass.

Refs #1 #9

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Schema.php

@@ -37,6 +37,29 @@ class Schema {
                 KEY student_id (student_id),
                 KEY instructor_id (instructor_id)
             ) {$charset};",
+
+			"CREATE TABLE {$prefix}us_offerings (
+                id               BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
+                instructor_id    BIGINT UNSIGNED NOT NULL,
+                kind             VARCHAR(20)     NOT NULL,
+                title            VARCHAR(191)    NOT NULL,
+                description      TEXT,
+                duration_minutes SMALLINT UNSIGNED DEFAULT NULL,
+                price_cents      INT UNSIGNED    NOT NULL DEFAULT 0,
+                currency         VARCHAR(3)      NOT NULL DEFAULT 'CAD',
+                billing_mode     VARCHAR(20)     NOT NULL DEFAULT 'one_time',
+                allow_weekly     TINYINT(1)      NOT NULL DEFAULT 0,
+                capacity         SMALLINT UNSIGNED DEFAULT NULL,
+                term_start       DATE            DEFAULT NULL,
+                term_end         DATE            DEFAULT NULL,
+                schedule_note    VARCHAR(191)    DEFAULT NULL,
+                is_active        TINYINT(1)      NOT NULL DEFAULT 1,
+                created_at       DATETIME        NOT NULL,
+                PRIMARY KEY (id),
+                KEY instructor_id (instructor_id),
+                KEY kind (kind),
+                KEY is_active (is_active)
+            ) {$charset};",
 		];
 	}
 }