feat: Take screenshots (#759)

## Summary

* **What is the goal of this PR?** Implements a take-screenshot feature
* **What changes are included?**

- Quick press Power button and Down button at the same time to take a
screenshot
- Screenshots are saved in `screenshots` folder

## Additional Context

- Currently it does not use the device orientation.

---

Example screenshots:


![screenshot-6771.bmp](https://github.com/user-attachments/files/25157071/screenshot-6771.bmp)

[screenshot-6771.bmp](https://github.com/user-attachments/files/25157071/screenshot-6771.bmp)


![screenshot-14158.bmp](https://github.com/user-attachments/files/25157073/screenshot-14158.bmp)

[screenshot-14158.bmp](https://github.com/user-attachments/files/25157073/screenshot-14158.bmp)


### AI Usage

Did you use AI tools to help write this code? _** YES

---------

Co-authored-by: Eliz Kilic <elizk@google.com>
Co-authored-by: Xuan Son Nguyen <son@huggingface.co>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Arthur Tazhitdinov <lisnake@gmail.com>

lib/I18n/I18nKeys.h

@@ -355,6 +355,7 @@ enum class StrId : uint16_t {
   STR_BOOK_S_STYLE,
   STR_EMBEDDED_STYLE,
   STR_OPDS_SERVER_URL,
+  STR_SCREENSHOT_BUTTON,
   // Sentinel - must be last
   _COUNT
 };