feat(plugin-form-builder): support translations

[quentinhermiteau]

What?

Adds i18n support to @payloadcms/plugin-form-builder.

This replaces hardcoded admin labels, descriptions, option labels, block labels, and field labels with translation keys under the plugin-form-builder namespace. It also adds English and French translation files and exports the plugin translations for external reuse or overrides.

Why?

The form builder plugin currently renders many admin UI strings directly in English. This makes the plugin inconsistent with Payload’s i18n support and with other plugins that already expose translated admin labels.

This change allows form builder UI text to be translated based on the active Payload admin language, while still allowing users to override plugin translations through config.i18n.translations.

How?

• Added @payloadcms/translations as a dependency of @payloadcms/plugin-form-builder.
• Added en and fr translation objects under packages/plugin-form-builder/src/translations.
• Merged plugin translations into the Payload config using the same pattern as plugin-redirects, with user-provided translations taking precedence.
• Replaced hardcoded form builder labels and admin descriptions with t('plugin-form-builder:...').
• Added translated labels for form field blocks, confirmation settings, email settings, upload settings, payment fields, and form submission payment metadata.
• Exported formBuilderTranslations so consumers can inspect or reuse the plugin translation object.

Testing

• Ran pnpm --filter @payloadcms/plugin-form-builder build
• Manually tested the plugin in a Payload app configured with French admin i18n and verified plugin translation keys can be resolved and overridden.

Fixes #