fix: support comma-separated application names in translate setup workflow

[Copilot]

The _translate-setup.yml reusable workflow only accepted a single application_name, causing the job to fail when a user passed multiple app names as a comma-separated string (e.g. frontend-app-learner-portal-enterprise, frontend-app-admin-portal).

Changes

• _translate-setup.yml: Parse application_name as a comma-separated list; validate each entry individually; filter the matrix to all matching apps
• Caller workflows (translate-json-source-strings.yml, seed-json-translations.yml, translate-po-source-strings.yml, seed-po-translations.yml): Updated application_name input descriptions to document comma-separated support

Before: entire comma-separated string treated as a single (invalid) app name → core.setFailed

After:

const selectedApps = appInput
  ? appInput.split(',').map(s => s.trim()).filter(Boolean)
  : [];
// validates and filters each app independently