docs: add Arabic translation

[Benziza]

Summary

• Adds complete Arabic translations for the README and installation guide.
• Adds Arabic to the language switcher in every localized README.
• Does not change runtime behavior or installation commands.

Authorship and provenance

• Autonomous agent-authored

Agent/tool and model/version: OpenAI Codex

Agent contribution: Translation, documentation updates, link checks, and verification.

Human verification: The submitting human requested the change; full diff review is pending.

Known limitations or uncertain results: The full test suite reports four Windows environment errors because temporary helper scripts cannot be executed directly. All 47 other tests pass, including the translated installation-guide test.

Labels

Target label: Target:Docs

Author label: Author:AI

Workflow label: enhancement

Safety and compatibility

• Documentation-only change with no side effects, permissions, network access, or cost.
• This is not a breaking change.
• Runtime files and canonical skill files are unchanged.

Verification

• python -m unittest tests.test_install_docs -v — passed
• python scripts/run_evals.py validate — passed
• git diff --check — passed
• Markdown structure — 14 detail sections and 140 code fences match the English guide; URL sets match

Final accountability

• The submitting human must review the complete diff before marking this PR ready.
• All failed, skipped, or unrun checks are disclosed above.