v0.5.3 — Fully localize the engine_started backend message

What's new

Follow-up to v0.5.2's app-wide language switcher: the one remaining English-only string generated by the backend is now fully localized too.

• The engine_started activity-log entry used to bake the phrase "N active rule(s)" directly into the event sent over the WebSocket, so it always showed up in English regardless of the GUI's selected language.
• The Python core now sends a structured rule count (rule_count) instead of a pre-formatted English sentence. The GUI renders it using its own locale files, so it now correctly reads e.g. "Engine started (3 active rule(s))" or "引擎已啟動（3 條規則啟用中）" depending on the selected language.
• No other backend-generated strings needed this treatment — the only other free-text field (rule_error's exception message) is inherently untranslatable runtime error text and was already wrapped in a translated sentence around it.

This closes the one known limitation noted in the v0.5.2 release: the entire GUI is now fully bilingual, front-end and backend-sourced text alike.

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新功能

接續 v0.5.2 的全應用程式語言切換：後端產生、原本唯一還是英文寫死的字串，這次也完整在地化了。

• 「引擎已啟動」這則活動紀錄，原本會把「N active rule(s)」這句英文直接寫死組進透過 WebSocket 傳送的事件內容，導致不管 GUI 選了哪種語言，這行都固定顯示英文。
• Python 核心現在改為傳送結構化的規則數量（rule_count），而不是組好的英文句子。GUI 端用自己的語言檔渲染這段文字，因此現在會依照所選語言正確顯示，例如「Engine started (3 active rule(s))」或「引擎已啟動（3 條規則啟用中）」。
• 其餘後端產生的字串不需要這樣處理——唯一另一個自由文字欄位（rule_error 的例外訊息）本身就是無法翻譯的執行期錯誤文字，且原本就已經包在翻譯好的句子裡顯示。

這次修正補上了 v0.5.2 版本說明裡提到的唯一已知限制：現在整個 GUI，不論是前端還是後端來源的文字，都已完整雙語化。