Guides and examples: email providers, i18n, monorepos, MJML and Beefree, upgrading to 0.3

[ivoIturrieta]

Stacked on the MJML and Beefree importers PR (#70), which is stacked on the 0.3.0 library PR (#69): it shows only the guides and examples. Merge it after both, with its base changed to main first. The repo's tests only run on pull requests into main or develop, so CI starts here once the base is main; until then, the validation below was run locally, with #70's head (which has #69's final head, bc81fd5) merged in.

What

• Email providers: the content-workflows example sends with 14 providers. Mailgun, Azure, MailerSend, Scaleway, Plunk, Lettermint, Brevo, Inbound and EUSend are added, each tested against mocked endpoints. Guide: email providers.
• i18n example: one template in English and Arabic with react-intl, react-i18next and next-intl, including right-to-left output. It runs in CI. Guide: translations and right-to-left, written for 0.3 (inline <FormattedMessage>/<Trans> children, right alignment by default in RTL, Tailwind's logical classes following the direction, a class provider such as <IntlProvider> around the root, and an async component failing a synchronous render).
• Migrating from MJML: leads with npx @unlayer/migrate <dir> --from mjml: what becomes editable blocks, what stays MJML's HTML, includes, MJML 3, what the check compares against. The hand mapping stays, for tuning the output.
• Migrating from Beefree (new): the JSON it reads, the HTML export to put beside it so the template is checked, ? for unverified, and the declared differences.
• Upgrading: what changes from 0.2 to 0.3 and what to check (16 items: a part that fails fails the render by default, the text block's markup, images sized in their slot, the editor's base stylesheet, the Provider, right-to-left alignment, async components and a <Suspense> around the template, how the plain text differs, React's ids, migrate's range, …), what else changed (a class component around the root is unwrapped), the new entries (Tailwind's logical classes follow the text direction; Markdown keeps raw HTML to an allowlist), and the 0.1 to 0.2 guide.
• Monorepos: one Elements copy, React resolution and workspaces (what two copies of React do with 0.3's renderer), previewing with a small render script.
• No unpublished packages: the guides don't mention the local preview package or the CLI commands that need it.
• READMEs: point to the Elements skill in unlayer/unlayer-skills, and list @unlayer/migrate as published, with its MJML and Beefree sources. The changelog only gets a line pointing to the upgrade guide (its 0.1.1 to 0.2.1 history is in @unlayer/react-elements 0.3.0: Tailwind, Markdown, code, fonts, async, codegen and editor-parity fixes #69).

Validation

• The merge of @unlayer/migrate: MJML and Beefree importers (--from mjml|beefree) #70's head had no conflicts. The packages' tests pass on the merged branch (react 1,540, migrate 361, from-react-email 344, convert-core 219, shared 126), and the typechecks are clean.
• content-workflows: typecheck and 13/13 tests pass. i18n: typecheck and 4/4 pass.
• A replay of the repo's CI workflow on a clean checkout, the new i18n step included, passes every step.
• The MJML and Beefree guides' output was checked by running the CLI on the committed fixtures with the merged build (MJML 19 ✓; Beefree 10 ✓ and 7 ?). --strict, includes outside the folder, MJML 3, unknown Beefree versions and the Elements version check were run before the merge, which doesn't change that code; migrate's tests for them pass.
• Each upgrade item was checked by rendering with 0.2.1 and with 0.3.0 (@unlayer/react-elements 0.3.0: Tailwind, Markdown, code, fonts, async, codegen and editor-parity fixes #69's final head for the ones this update adds: the plain text, a class component around the root, error boundaries, a <Suspense> around the template, Tailwind's logical classes in right-to-left), and so were the i18n and monorepo guides' statements about errors, class providers and two copies of React.
• Every relative link in the changed docs resolves.