Add Tamil (ta) translation of accessibility best practices guide

[ajaitech]

Translates _articles/accessibility-best-practices-for-your-project.md into Tamil, added at _articles/ta/accessibility-best-practices-for-your-project.md.

This is currently the only article missing from every translation folder in the repo, ta included, so this closes that gap for Tamil readers.

What this change does

• One new file, 301 lines. No existing files are modified.
• Front matter uses lang: ta with a translated title and description. class, order and image are left byte-identical to the English source so the site build, navigation order and social card are unaffected. The source's untranslated: true flag is intentionally not carried over.
• Structure matches the English source exactly: 41 headings at the same levels, 126 list items at the same nesting depths, and all 30 external links preserved with their original targets.
• Translator credit follows the convention already used in _articles/ta/maintaining-balance-for-open-source-maintainers.md (GitHub handle in the Contributors section).

Why it adds value

Accessibility is the one guide with no translations at all, and Tamil has one of the larger developer populations without it. Making this article readable in Tamil lowers the barrier for maintainers who would otherwise skip the topic entirely.

A note on register

This translation is written in colloquial spoken Tamil (Kongu / Coimbatore usage) rather than the formal written register used in the other _articles/ta/ files. That is a deliberate choice rather than an oversight: it reflects how a great many Tamil-speaking developers actually read and talk about this material, and technical terms are left in English as they are in everyday usage.

I'm aware this differs from the existing Tamil articles and I'm very happy to discuss it. If maintainers would prefer consistency across the ta folder, I'll gladly revise toward the formal register.

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