i18n: Add Persian (fa) translation

[Parviz-sudo]

Summary

Adds Persian (fa) localization support to CachyOS Hello.

• Added i18n/fa/cachyos_hello.ftl — Persian translation of all main UI strings (tweaks, DNS settings, troubleshooting, main page, etc.)
• Added data/pages/fa/readme — Persian translation of the "Read me" page
• Added data/pages/fa/involved — Persian translation of the "Get involved" page
• Updated ui/cachyos-hello.glade — added "فارسی" entry to the language selector combo box (sorted by language code, between eu and fr)

Notes

• All Fluent placeables (e.g. {$package_name}, {$protocol}, {$tweak}) were preserved exactly as in the source strings.
• Persian is a right-to-left (RTL) language. I tested the language switcher and main strings, but haven't been able to verify every page/widget for RTL layout edge cases — feedback and testing from maintainers/other Persian speakers is welcome.
• Comments in the .ftl file were left in English to match the convention used in other language files.

Testing

• Built and ran locally via meson/ninja install.
• Switched the language selector to فارسی (fa) and confirmed the main UI, tweaks page, and DNS settings page update correctly.
• Verified the "Read me" and "Get involved" pages render the translated text.