add Russian translation

[xtotdam]

Description

Add complete Russian (ru) language support for BentoPDF.

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

🧪 How Has This Been Tested?

Did everything as required in the checklist in TRANSLATION.md

Checklist:

• Verified output manually
• Tested with relevant sample documents or data
• Wrote Vite Test Case (if applicable)

Expected Results:

• All UI renders in Russian when visiting http://localhost:5173/ru/
• Russian option appears in the language switcher
• npm run build generates dist/ru/ directory

Actual Results:

• Homepage, about, contact, FAQ, and tool pages all render correctly in Russian
• Russian is selectable from the footer language switcher
• Static pages generated in dist/ru/ after build

Checklist:

• I have signed the Contributor License Agreement (CLA) or my organization has signed the Corporate CLA
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[xtotdam]

I have read the CLA Document and I hereby sign the CLA

[alam00000]

Thank you!