Remove manual polish scenario UI; rely on auto AppContext only

- Hide AppContext chip and remove manual override from keyboard
- Remove polish scenario picker and custom system prompt from settings
- Remove scenario section from onboarding
- Translation prompt uses auto-detected AppContext instead of polish scenario
- Delete ScenarioPrompt, ScenarioStyleDirective, PolishScenario, and related views

Co-authored-by: Rocky <hkgood@users.noreply.github.com>

OSGKeyboardShared/Services/AppGroupStore.swift

@@ -31,7 +31,6 @@ public struct AppGroupStore: @unchecked Sendable {
         static let providerId      = "config.providerId"
         static let baseURL         = "config.baseURL"
         static let model           = "config.model"
-        static let systemPrompt    = "config.systemPrompt"
         static let modeId          = "config.modeId"
         static let localeId        = "config.localeId"
         static let engineMode       = "config.engineMode"
@@ -45,7 +44,6 @@ public struct AppGroupStore: @unchecked Sendable {
         // the `translationEnabled` Bool accessor below is kept as a
         // computed shim for source compatibility.
         static let translationTargetLocaleId = "config.translationTargetLocaleId"
-        static let polishScenarioId = "config.polishScenarioId"
         static let handednessPreference = "config.handednessPreference"
         // v0.3.0: polish intensity (off / light / medium / heavy).
         static let polishIntensity = "config.polishIntensity"
@@ -79,10 +77,6 @@ public struct AppGroupStore: @unchecked Sendable {
         defaults.string(forKey: Key.model) ?? LLMProvider.provider(id: providerId).defaultModel
     }
 
-    public var systemPrompt: String {
-        defaults.string(forKey: Key.systemPrompt) ?? Self.defaultSystemPrompt(for: providerId)
-    }
-
     public var modeId: String {
         defaults.string(forKey: Key.modeId) ?? "polish"
     }
@@ -138,11 +132,6 @@ public struct AppGroupStore: @unchecked Sendable {
             ?? TranslationLanguageCatalog.offLocaleId
     }
 
-    public var polishScenarioId: String {
-        let stored = defaults.string(forKey: Key.polishScenarioId)
-        return PolishScenarioCatalog.resolve(stored ?? PolishScenarioCatalog.defaultId).id
-    }
-
     /// Bottom-row key order on the keyboard extension.
     public var handednessPreference: HandednessPreference {
         HandednessPreference.fromStored(defaults.string(forKey: Key.handednessPreference))
@@ -193,12 +182,6 @@ public struct AppGroupStore: @unchecked Sendable {
         AppGroupConfigDarwin.postConfigChanged()
     }
 
-    public func setPolishScenarioId(_ id: String) {
-        let resolved = PolishScenarioCatalog.resolve(id).id
-        defaults.set(resolved, forKey: Key.polishScenarioId)
-        AppGroupConfigDarwin.postConfigChanged()
-    }
-
     public func setHandednessPreference(_ preference: HandednessPreference) {
         defaults.set(preference.rawValue, forKey: Key.handednessPreference)
         AppGroupConfigDarwin.postConfigChanged()
@@ -229,25 +212,6 @@ public struct AppGroupStore: @unchecked Sendable {
         return localModeCloudPolishEnabled
     }
 
-    /// Whether the keyboard top-bar scenario chip should render.
-    public var isPolishScenarioChipVisible: Bool {
-        if engineMode == "cloud" { return true }
-        return localModeCloudPolishEnabled
-    }
-
-    /// System prompt for the polish pipeline honoring scenario selection.
-    public func resolvedPolishSystemPrompt(providerId: String? = nil) -> String {
-        if PolishScenarioCatalog.isCustom(polishScenarioId) {
-            return systemPrompt
-        }
-        let pid = providerId ?? self.providerId
-        return ScenarioPrompt.make(
-            scenarioId: polishScenarioId,
-            providerId: pid,
-            uiLanguage: uiLanguage
-        )
-    }
-
     /// Polish vs translate-and-polish for the active pipeline.
     public var polishModeForPipeline: PolishingService.PolishMode {
         isTranslationEffective
@@ -365,32 +329,4 @@ public struct AppGroupStore: @unchecked Sendable {
             model: model
         )
     }
-
-    // MARK: - Defaults
-
-    /// Per-provider default system prompt. We bias the prompt by the
-    /// provider's *primary* language so Chinese LLMs naturally return
-    /// Chinese for Chinese input, and English LLMs stay terse.
-    public static func defaultSystemPrompt(for providerId: String) -> String {
-        switch providerId {
-        case "zhipu", "moonshot", "qwen", "deepseek":
-            return """
-            你是一位语音输入润色助手。请将用户的口述改写为干净的中文(或英文)书面文字:
-            1) 保留原意,不编造事实;保持输入语言。
-            2) 添加恰当的标点、大小写、段落。
-            3) 当用户枚举"第一…第二…第三…"时,使用 markdown 列表。
-            4) 简洁,不超出原长 1.5 倍;可去掉无意义的口头禅(嗯、啊、那个)。
-            5) 只输出润色后的正文,不要解释、不要加引号。
-            """
-        default:
-            return """
-            You are a voice-input polishing assistant. The user has spoken informally; rewrite their dictation as clean written text:
-            1) Preserve the user's original intent and meaning; do not invent facts.
-            2) Add proper punctuation, capitalization, and paragraph breaks.
-            3) When the user enumerates items ("first ... second ... third"), output a markdown list.
-            4) Keep the output concise — do not exceed 1.5x the spoken length. Drop filler words (um, uh, like).
-            5) Output in the same language as the input. No quotes, no explanation, no preamble.
-            """
-        }
-    }
 }