Add Arabic localization for exercise instructions

[SMSMy]

Adds Arabic (ar) translations for all exercise instructions.

What's included

• data/exercises.schema.json: ar added to both languageMap and languageStepsMap.
• data/exercises.json: every one of the 1,324 exercises now has instructions.ar (full paragraph) and instruction_steps.ar (ordered step list) — 9,034 Arabic texts in total.
• index.html: embedded EXERCISES regenerated with Arabic; the interactive browser gets an Arabic tab, and Arabic steps render with dir="rtl".
• README.md: language count updated to 11, Arabic added to every language list.
• scripts/validate-schema.mjs + .github/workflows/validate.yml: schema validation (ajv, JSON Schema 2020-12) runs automatically on every push/PR.

Verification evidence

• No English fallbacks: a literal comparison of instructions.ar vs instructions.en and instruction_steps.ar vs instruction_steps.en across all 1,324 exercises returns 0 identical pairs — every Arabic text is a real translation, not a copied fallback.
• Schema: node scripts/validate-schema.mjs → ✓ valid — 1324 exercises against exercises.schema.json (now enforced by CI).

Translation methodology

• Initial translation produced with AI assistance, then human-reviewed over three rounds against a unified Arabic style guide (gym-appropriate terminology, direct instructional tone, no literal translations).
• Automated consistency checks applied to all 9,034 texts (forbidden literal phrases = 0; remaining Latin characters are only equipment attachment names such as D/V/Y).

Notes

• add_ar_placeholders.mjs (the one-off migration helper) was removed from the PR after review.
• Media (images/videos) is unchanged — this PR touches texts only.

[SMSMy]

Review feedback addressed + verification summary

All review notes from the discussion have been implemented:

Item	Status
No silent English fallbacks — instructions.ar never equals instructions.en	✅ verified across all 1,324 exercises (paragraph and steps compared literally, enforced in CI)
add_ar_placeholders.mjs (one-off migration helper)	✅ removed from the PR
Interactive browser (index.html) — embedded EXERCISES regenerated with Arabic	✅ Arabic tab added, steps render with dir="rtl"
RTL	✅ applies to the whole instructions container, not only the steps list
README.md	✅ 11 languages everywhere (field table, JSON sample, Python/JS examples, TypeScript interface)
SQL generators (index.html, setup.html)	✅ instructions_fr + instructions_ar exported in all four dialects — also fixes the pre-existing gap that stopped at instructions_ko
Language tabs	✅ 11 tabs scroll horizontally (overflow-x: auto) and the active tab is centered into view on mobile (direction-agnostic scroll delta — scrollIntoView({inline:'center'}) misses in RTL containers)
CI	✅ schema validation (ajv ^8) + two permanent content-integrity checks (no verbatim English fallbacks, no forbidden literal phrases) run on every push/PR

Verification

• node scripts/validate-schema.mjs → ✓ valid + ✓ no English fallbacks + ✓ no forbidden literal phrases + ✓ all checks passed
• CI on the latest commit: schema — completed/success → https://github.com/SMSMy/exercises-dataset/actions/runs/32899941113/job/97971150221
• Visual check in a headless browser (desktop 1280px and mobile 390px): grid, modal, 11 language tabs (scroll working, Arabic selected), RTL steps (numbers on the right, text right-aligned), and the LTR revert for other languages — no horizontal overflow on page or modal.

Scope note

data/exercises.json structure and the Arabic translation texts themselves are untouched — this PR only adds integration, docs, and checks around them.

Ready for review; happy to adjust anything.

[SMSMy]

Latest update on this branch:

• Narrowed RTL scope: dir="rtl" now applies only to the translated
  text element (the steps list), while the "Instructions" heading and
  the language tab bar stay LTR in every state. Verified across Arabic /
  French / English: tab order stays fixed, and only the text direction
  changes.
• Note: I noticed Add Arabic (RTL) instructions + RTL handling #81 targets the same goal (adding Arabic support).
  Happy for the maintainer to review both and use whichever fits the
  project better — that call is entirely yours.
• CI on the latest commit: passing ✅

Before the fix: the tab bar used to flip with the text.
After: