fix(validation): validate lang parameter against supported languages keys (JhaSourav07#1889)

## Description

Fixes JhaSourav07#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

- [x] npm run format
- [x] npm run lint
- [x] npm run test
- [x] npm run typecheck
- [x] 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

Author: JhaSourav07

lib/i18n/badgeLabels.ts

@@ -72,6 +72,11 @@ export const labels: Record<string, BadgeLabels> = {
   },
 };
 
+export const supportedLanguages = Object.keys(labels) as [
+  keyof typeof labels,
+  ...(keyof typeof labels)[],
+];
+
 export function getLabels(lang: string = 'en'): BadgeLabels {
   return labels[lang.toLowerCase()] || labels['en'];
 }

lib/validations.ts

@@ -1,5 +1,5 @@
 // lib/validations.ts
-
+import { supportedLanguages } from './i18n/badgeLabels';
 import { z } from 'zod';
 import {
   isValidHex,
@@ -188,7 +188,7 @@ export const streakParamsSchema = z.object({
   hide_title: z.string().optional().transform(toBooleanFlag),
   hide_background: z.string().optional().transform(toBooleanFlag),
   hide_stats: z.string().optional().transform(toBooleanFlag),
-  lang: z.string().optional().default('en'),
+  lang: z.enum(supportedLanguages).catch('en').default('en'),
   // Unknown view values fall back to the default dashboard view.
   view: z.enum(['default', 'monthly']).catch('default').default('default'),
   // Invalid delta formats fall back to percentage mode.