docs: add Persian (fa) docs site localization

[raminjafary]

Issue for this PR

Closes#34240

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds a Persian (Farsi) fa locale to the docs site (packages/web), matching the existing locales. The README is tracked separately (#31771 / #31773), so this PR deliberately doesn't touch it.

• Adds fa (RTL, fa-IR) to astro.config.mjs — locale entry + the four sidebar group labels
• Wires fa into packages/web/src/i18n/locales.ts — docs locale list, alias map, Accept-Language matching
• Translates all 34 docs pages into packages/web/src/content/docs/fa/
• Adds docs UI strings packages/web/src/content/i18n/fa.json (same keys as en.json)
• Adds .opencode/glossary/fa.md

I used the existing Arabic (ar) RTL locale as the structural reference and kept all code blocks, commands, paths, imports, and product names unchanged.

How did you verify your code works?

• The fa docs folder has the same 34 filenames as every other locale
• fa.json has the same keys as en.json with no leftover English values
• Relative import/asset paths use the correct depth for the nested dir (../../../../config.mjs, ../../../assets)
• No stray Arabic glyphs (ك/ي); uses Persian ک/ی
• node --check packages/web/astro.config.mjs passes

Screenshots / recordings

_Docs-only change;

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

I verified every claim in it against your branch diff vs dev (38 files: the fa/ doc pages + astro.config.mjs, locales.ts, i18n/fa.json, .opencode/glossary/fa.md) — all accurate.

It's also saved at scratchpad/pr-body.md if you'd rather copy from a file.

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[github-actions]

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