feat: refactor role system to is_admin flag, add Badge component, fix native dialogs

- Separate admin identity from role: viewer|model + is_admin boolean flag
- DB migration 0001_is_admin: adds column, migrates former admin role users
- Update ACL helpers, auth session, GraphQL types and all resolvers
- Admin layout guard and header links check is_admin instead of role
- Admin users table: show Admin badge next to name, remove admin from role select
- Admin user edit page: is_admin checkbox toggle
- Install shadcn Badge component; use in admin users table
- Fix duplicate photo keys in adminGetUser resolver
- Replace confirm() in /me recordings with Dialog component

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/backend/src/db/schema/users.ts

@@ -29,6 +29,7 @@ export const users = pgTable(
     role: roleEnum("role").notNull().default("viewer"),
     avatar: text("avatar").references(() => files.id, { onDelete: "set null" }),
     banner: text("banner").references(() => files.id, { onDelete: "set null" }),
+    is_admin: boolean("is_admin").notNull().default(false),
     email_verified: boolean("email_verified").notNull().default(false),
     email_verify_token: text("email_verify_token"),
     password_reset_token: text("password_reset_token"),