beta-260623: Add EasyControl/Colorize docs and i18n

Introduce EasyControl (and its Colorize variant) documentation and UI help across multiple locales. Adds guidebook entries (EN/CN/JA/KO), new webui explanation pages (easycontrol + colorize) and updated guide field metadata (_fields.json) exposing EasyControl settings (use_easycontrol, easycontrol_drop_p, easycontrol_cond_noise_max, cond_res_scale). Wire up frontend i18n by adding ja/ko language files and updating App.vue, useI18n and i18n index; also update loader.py and related build info. Also document a test-easycontrol make target for image-conditioned inference.