docs: add Arabic documentation edition

[m0hamed-ux]

Adds an Arabic documentation edition at /ar/, with Modern Standard Arabic terminology and the existing language selector, navigation, and translation notices.

Fixes #3665

This contains all 52 pages currently eligible for translation, Arabic style-guide and glossary inputs, and generated notices. The API reference and migration guide remain English under the existing registry policy. The root README translation is a separate local review draft and is not included here. No SDK runtime code or dependencies change.

Generation and review

Codex assisted with contribution research, the Arabic style guide and glossary, and the documentation translations. No Anthropic API key was used: Codex generated drafts that a local adapter supplied through the repository's Translator interface to translate_page. The official tooling restored code fences, pinned English heading IDs, validated structure, and wrote source-section provenance. The translator itself was not modified. This differs from the documented Claude API command; maintainer feedback on that method is welcome, including regeneration with the standard tool if preferred.

The contributor reviewed the Arabic preview and approved proceeding with this PR. English remains authoritative, and future corrections should go through language inputs and regeneration.

Validation

• Translation status: 0 missing, 0 outdated, 53 current (52 pages plus notices), 0 removable.
• All translations passed the repository's code, link-target, heading, list/table, marker, and placeholder validation.
• uv run --frozen pytest tests/docs -q: 49 passed.
• English and Arabic Zensical builds with --strict: passed without issues.
• API render-order and built-site cross-reference checks: passed.
• Markdown lint, glossary/registry formatting, README snippet check, and whitespace checks: passed.
• Built Arabic HTML has right-to-left direction, with left-to-right code styles; 4,783 local links/anchors passed a supplemental check.

Only English and Arabic sites were built. Updating the available-language list marks the other editions' translations.md outdated until their usual regeneration.

Draft scope

Issue #3665 currently has no assignee or help wanted label. This draft makes the prepared edition available for scope and workflow discussion; it does not imply maintainer approval. The issue originally proposed a smaller starting contribution, and this work can be split into an initial homepage/Get started set followed by topical batches if preferred.

[github-actions]

This PR has been closed automatically. It's still a draft, but we close those early so you don't put in more time only to have it closed the moment you mark it ready.

This repo only keeps pull requests open when they come from a maintainer, or from a contributor a maintainer has assigned to the linked issue, and you aren't currently assigned to #3665.

If a maintainer assigns you to #3665, this PR reopens on its own and there's nothing more you need to do here. Assignment is a maintainer call based on capacity; comments that only ask to be assigned don't factor in. What does help is engaging on the issue itself by confirming the repro, explaining why it matters for your use case, or describing the approach you'd take.

You're welcome to keep pushing commits here (just avoid force-pushing, since GitHub can't reopen a rewritten branch), but that on its own won't get the PR reviewed or the issue assigned, and realistically most auto-closed PRs stay closed. There's no need to open a new PR either way.

CONTRIBUTING.md has the full reasoning, but in short:

• We're a small team with very little capacity to review community PRs right now.
• Many recent PRs are AI-generated with little human review, and reviewing one carefully still costs a maintainer as much time as it ever did. A well-described issue is usually more useful to us than the code.

Maintainers: reopen, remove missing-issue-link, or add bypass-issue-check to override.