feat(i18n): add the Slovak (sk-SK) panel locale (#6889)

Adds a complete Slovak translation of every panel and bot string, registers
sk-SK in the language picker (a browser set to sk now lands on it instead of
English) and loads Ant Design's Slovak locale. The locale count in the READMEs,
docs and contributor guides moves from 13 to 14.

README.md

@@ -41,7 +41,7 @@ Built as an enhanced fork of the original X-UI project, 3X-UI adds broader proto
 - **RESTful API** with scoped, optionally expiring tokens and an in-panel API reference.
 - **Installable panel (PWA)** — pin 3X-UI to a desktop or phone home screen.
 - **Flexible storage** — SQLite (default) or PostgreSQL.
-- **13 UI languages** with dark and light themes.
+- **14 UI languages** with dark and light themes.
 - **Fail2ban integration** for enforcing per-client IP limits.
 
 ## Screenshots
@@ -177,9 +177,9 @@ The complete list is on the [environment variables reference](https://docs.sanae
 
 ## Supported Languages
 
-The panel UI is available in 13 languages:
+The panel UI is available in 14 languages:
 
-English · فارسی · العربية · 中文（简体） · 中文（繁體） · Español · Русский · Українська · Türkçe · Tiếng Việt · 日本語 · Bahasa Indonesia · Português (Brasil)
+English · فارسی · العربية · 中文（简体） · 中文（繁體） · Español · Русский · Українська · Türkçe · Tiếng Việt · 日本語 · Bahasa Indonesia · Português (Brasil) · Slovenčina
 
 ## Contributing