Locale-aware date, currency & number formatting

[rohitdash08]

Improve global usability with locale-aware formatting.

Acceptance Criteria

• Production ready implementation
• Includes tests
• Documentation updated

[a827681306]

/attempt #131

I'll implement this with full test coverage and documentation. PR incoming shortly.

[zhaog100]

/attempt #131

Implementing locale-aware formatting:

Backend:

• Locale detection from user profile
• Date formatting by locale (ISO, US, EU, IN)
• Currency formatting with proper symbols and decimals
• Number formatting (thousands separators)

Frontend:

• Locale context/provider
• Formatted display components
• User locale preference setting

Starting immediately.