feat(translation): add post-ASR translation mode for cloud engine

Adds an opt-in translation pipeline that reuses the existing
PolishingService + LLMClient + AppGroupStore chain. Translation is
implemented as a new PolishMode (.translate(targetLocaleId:)); all
existing call sites are unchanged.

Settings:
- New TranslationPickerRow in the language tab (Toggle + 10-locale
  picker: en/zh-Hans/zh-Hant/ja/ko/fr/de/es/ru/pt), persisted to the
  App Group so the keyboard extension can read it during live dictation.
- 5 new strings per language (en + zh-Hans).

Keyboard:
- New TranslationChip on the top bar to the right of LocaleChip;
  same Menu pattern, lets users toggle or quickly switch target
  language without leaving the keyboard.
- PolishingService dispatches .translate with a parameterised prompt
  (en/zh variants selected by provider id); PolishingService.error
  gains a translationNotAvailable case so local-engine users get a
  clear inline warning when the toggle is on but cloud is off.
- 6 new strings per language (en + zh-Hans) for the chip + banner.

Local engine policy:
- Translation is cloud-only by design (local engine stays ASR-only
  to honour the no-roundtrip promise). Chip shows a 'cloud required'
  state and raw transcript still inserts on failure — no data loss.

Build:
- OSGKeyboardShared adds TranslationLanguage enum (10 locales) and
  TranslationPrompt factory.
- 4 new files, 9 modified. xcodebuild scheme=OSGKeyboard
  config=Debug destination=iPhone 17 Simulator: BUILD SUCCEEDED
  (0 warning, 0 error).

Also pins DEVELOPMENT_TEAM in project.yml for TestFlight uploads
(3 targets; Team X329MZU23S).

OSGKeyboardShared/Services/TranslationPrompt.swift

@@ -0,0 +1,61 @@
+// TranslationPrompt.swift
+// OSGKeyboard · Shared
+//
+// Builds the system prompt the LLM sees when the user has the
+// translation toggle on. Re-uses the same per-provider "primary
+// language" split the polish prompt uses (`AppGroupStore.defaultSystemPrompt`)
+// so Chinese-native LLMs (DeepSeek, Qwen, GLM, Moonshot) get a Chinese
+// prompt and English-native LLMs (OpenAI) get an English one — the LLM
+// is most reliable when the instructions are written in its strongest
+// language.
+//
+// The "translate AND polish" blend is intentional: ASR transcripts are
+// noisy (homophone errors, broken segmentation, dropped particles), so
+// the prompt asks the model to clean the noise while translating.
+// Keeping those two concerns in one prompt matches how our existing
+// polish prompt already mixes "preserve meaning" with "fix punctuation /
+// drop filler".
+
+import Foundation
+
+public enum TranslationPrompt {
+
+    /// Build the translate-and-polish system prompt.
+    ///
+    /// - Parameters:
+    ///   - target: target language entry resolved via `TranslationLanguageCatalog`.
+    ///   - providerId: provider preset id (e.g. `"deepseek"`, `"openai"`);
+    ///     drives the language the prompt is written in.
+    public static func make(target: TranslationLanguage, providerId: String) -> String {
+        let isChineseNative = ["zhipu", "moonshot", "qwen", "deepseek"].contains(providerId)
+        return isChineseNative ? chinesePrompt(target: target) : englishPrompt(target: target)
+    }
+
+    // MARK: - Chinese prompt (for DeepSeek / Qwen / GLM / Moonshot)
+
+    private static func chinesePrompt(target: TranslationLanguage) -> String {
+        """
+        你是一位语音输入翻译与润色助手。用户用 ASR 转写了一段可能含噪声的口述:
+        1) 先识别原话的主要语言(若不确定则按用户给定的方向处理);
+        2) 将内容翻译为「\(target.promptLanguageName)」,保留原意,不增删事实、不臆测;
+        3) 顺带修复 ASR 噪声(同音错字、漏字、断句错乱),让译文读起来自然;
+        4) 保留枚举结构(第一…第二…),使用「\(target.promptLanguageName)」的列表惯例;
+        5) 简洁,不超过原文 1.5 倍;去掉无意义的口头禅(嗯、啊、那个);
+        6) 只输出译文正文,不要解释、不要加引号、不要前缀"以下是翻译"。
+        """
+    }
+
+    // MARK: - English prompt (for OpenAI / OpenAI-compatible non-Chinese)
+
+    private static func englishPrompt(target: TranslationLanguage) -> String {
+        """
+        You are a voice-input translation and polishing assistant. The user has spoken informally and the transcript may contain ASR noise:
+        1) Identify the input language; if unclear, assume the user wants translation INTO \(target.promptLanguageName);
+        2) Translate the content INTO \(target.promptLanguageName), preserving meaning; do not invent facts or omit content;
+        3) Fix ASR noise (homophone errors, missing characters, broken segmentation) so the translation reads naturally;
+        4) Preserve enumeration ("first ... second ...") using \(target.promptLanguageName) list conventions;
+        5) Keep it concise — no longer than 1.5x the spoken length; drop filler words (um, uh, like);
+        6) Output ONLY the translation. No quotes, no preamble, no explanation.
+        """
+    }
+}