feat(i18n): add Polish language support (#14080)

It's my first time making a pull request to any repo. If there are any
issues, let me know.

## Summary
Adds Polish language support. Translation is 98% complete (10,447/10,646
words).

## Changes
- Added `pl` to Language type
- Added Polish to SUPPORTED_LANGUAGES with lazy loading

The `pl.json` file already exists in the repo with good translation
coverage. Some AI-related strings are not yet translated but will fall
back to English.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **New Features**
* Added Polish language support to the application, including localized
language name, native language name, and flag emoji.

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settings.</sub>

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/i18n/src/resources/index.ts

@@ -8,6 +8,7 @@ export type Language =
   | 'es'
   | 'es-AR'
   | 'es-CL'
+  | 'pl'
   | 'de'
   | 'ru'
   | 'ja'
@@ -89,6 +90,12 @@ export const SUPPORTED_LANGUAGES: Record<
     flagEmoji: '🇨🇱',
     resource: () => import('./es-CL.json'),
   },
+  pl: {
+    name: 'Polish',
+    originalName: 'Polski',
+    flagEmoji: '🇵🇱',
+    resource: () => import('./pl.json'),
+  },
   de: {
     name: 'German',
     originalName: 'Deutsch',