Feat: Implement i18n support for multi-language accessibility

### Describe the feature

**Is there an existing issue for this?**

* [x] I have searched the existing issues

**What happened?**
**Lack of Internationalization (i18n) Support**
The application currently uses hardcoded English strings throughout the frontend codebase. This prevents the interface from being translated into other languages, limiting accessibility for non-English users and blocking global community contributions.

**File:** `frontend/src` (General)

**Step Action**
| Step | Action |
| :--- | :--- |
| 1 | Open the PictoPy source code (e.g., `LeftSidebar.tsx` or `Settings.tsx`). |
| 2 | Locate UI elements like buttons or labels. |
| 3 | **Result:** Observe that text is hardcoded (e.g., `Save`) instead of using translation keys (e.g., `{t('save')}`). |
| 4 | Open the PictoPy application and go to Settings. |
| 5 | **Result:** There is no option to switch the interface language. |

**Suggested Solution**
Integrate a library like `i18next` and `react-i18next`. Extract hardcoded strings into locale files (e.g., `en.json`) to allow the community to submit translations for other languages.

**Record**

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### Record

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- [x] I want to work on this issue