Feature: Add Cloudflare image format setting

[roboes]

Description

PhastPress counterpart to kiboit/phast#22, which contains the full context and core logic.

Adds an img-cloudflare-format setting (off / webp / avif) to the WordPress admin panel, allowing users to configure modern image format serving behind Cloudflare. Defaults to off, preserving existing behaviour.

Changes

• PluginConfiguration::getDefaultAdminPanelSettings() - adds 'img-cloudflare-format' => 'off'.
• PhastConfiguration::get() and getForHTMLSnippets() - maps the setting to $phastConfig['images']['cloudflare-image-format'].
• Translations::DATA - adds UI label, per-option descriptions, and a tip linking to the Cloudflare Vary for Images documentation.
• Translations::__construct() - fixes PHP 8.1+ deprecation: isset() was called with $this->locale (which is null before assignment) as the array offset; changed to use the $locale parameter instead. No behavior change; compatible with PHP 7.4-8.5.

Notes

The PHP side is complete. For the admin panel UI, the Vue source appears to live in a private SDK repo not accessible from the public phast or phastpress repos.

To render the img-cloudflare-format setting as a three-option select (off / webp / avif), a new Vue component would be needed. Two options to consider:

1. If the SDK source can be shared or the maintainer can add a select component, a three-option dropdown would give the cleanest UX.
2. Alternatively, two boolean toggles (img-cloudflare-webp and img-cloudflare-avif) could replace the single select - this fits the existing UI without any new components.

Happy to go either way, but would need guidance or access to the SDK source to proceed with option 1.