feat: add a Keep it free sponsor button to the top nav (#427)

Adds a prominent Keep it free sponsor button to the top nav, linking to https://github.com/sponsors/snapotter-hq. Solid orange pill on desktop (left of the avatar), orange heart icon on mobile. Opens in a new tab with rel=noopener noreferrer, so no referrer or user data leaks, and it adds no passive network activity (offline-mode compatible). Fires an opt-in, property-less sponsor_clicked analytics event. Adds sidebar.sponsor and a11y.sponsorLink across all 21 locales.

Claude-Session: https://claude.ai/code/session_01DnYLLA5z4Uf1GDeEPENVgr

packages/shared/src/i18n/ru.ts

@@ -3847,6 +3847,7 @@ export const ru: TranslationKeys = {
     connectionError: "Ошибка подключения",
   },
   sidebar: {
+    sponsor: "Пусть будет бесплатным",
     tools: "Инструменты",
     grid: "Сетка",
     automate: "Автоматизация",
@@ -3866,6 +3867,7 @@ export const ru: TranslationKeys = {
     mobileNavSettings: "Настройки",
   },
   a11y: {
+    sponsorLink: "Поддержать SnapOtter на GitHub Sponsors",
     skipToContent: "Перейти к основному содержимому",
     openSidebar: "Открыть боковую панель",
     closeSidebar: "Закрыть боковую панель",