fix(validation): validate lang parameter against supported languages keys

[Thacker-Meet]

Description

Fixes #1796

Changes Made

• Added supportedLanguages derived from translation keys in badgeLabels.ts
• Updated streakParamsSchema to validate lang using z.enum()
• Added .catch('en') fallback behavior for unsupported language inputs
• Preserved default English fallback behavior

Verification

• npm run format
• npm run lint
• npm run test
• npm run typecheck
• Verified invalid lang values fall back to en

Result

• Valid language inputs continue to work correctly
• Unsupported language values now safely fall back to English (en)
• Prevents downstream localization lookup failures during SVG generation

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[github-actions]

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