Complete Arabic localization with UI strings and RTL configuration

[aslamalkarywk7]

Summary

This PR introduces full Arabic localization for the InvokeAI documentation suite. It features the translation of the core documentation pages, UI localization strings, and configures the layout for Right-to-Left (RTL) reading orientation.

• Kind of change: Documentation (docs) / i18n
• The "Why": To make InvokeAI accessible to the Arabic-speaking developer and creator community, expanding the project's global reach.
• The "How":
  • Translated and added 62 MDX documentation files under docs/src/content/docs/ar/.
  • Added core UI localization keys inside src/content/i18n/ar.json.
  • Configured the Arabic locale metadata with dir: 'rtl' inside astro.config.mjs.
  • Included all localized high-resolution asset images and banners.

Related Issues / Discussions

• Supersedes and replaces the closed PR Translate InvokeAI documentation to Arabic for Arab developers #9282.

QA Instructions

I have thoroughly tested the documentation build locally to ensure a seamless layout:

1. Ran the local Astro Starlight development server using pnpm dev.
2. Verified the entire Arabic (/ar/) documentation path.
3. Confirmed that the typography, sidebar navigation, and search layout adapt perfectly to the Right-to-Left (RTL) alignment.
4. Checked that all absolute/relative image paths render properly without broken links.

Merge Plan

This is a large PR containing documentation files and assets only. It does not touch any core application logic, DB schemas, or code repositories. It can be safely merged once the documentation CI checks pass.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• ❗Changes to a redux slice have a corresponding migration
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)