feat(schema): add is_super_user to staff table (GRO-201)

Add boolean is_super_user column (default false) to staff table.
Update Staff interface in shared types.
Mark first manager as super user in both seed modes.
Update test fixtures to include isSuperUser field.

Co-authored-by: groombook-ci[bot] <ci@groombook.bot>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

packages/db/src/schema.ts

@@ -159,6 +159,8 @@ export const staff = pgTable("staff", {
   // Better-Auth user ID — links staff business record to auth identity
   userId: text("user_id").references(() => user.id, { onDelete: "set null" }),
   role: staffRoleEnum("role").notNull().default("groomer"),
+  // Super users bypass appointment-booking restrictions and access admin panels
+  isSuperUser: boolean("is_super_user").notNull().default(false),
   active: boolean("active").notNull().default(true),
   // Token for iCal calendar feed subscription (no auth required)
   icalToken: text("ical_token").unique(),