refactor: remove OMO common config two-layer merge system

Each OMO provider now stores its complete configuration directly in
settings_config.otherFields instead of relying on a shared OmoGlobalConfig
merged at write time. This simplifies the data flow from a 4-tuple
(agents, categories, otherFields, useCommonConfig) to a 3-tuple and
eliminates an entire DB table, two Tauri commands, and ~1700 lines of
merge/sync code across frontend and backend.

Backend:
- Delete database/dao/omo.rs (OmoGlobalConfig struct + get/save methods)
- Remove get/set_config_snippet from settings DAO
- Remove get/set_common_config_snippet Tauri commands
- Replace merge_config() with build_config() in services/omo.rs
- Simplify OmoVariant (remove config_key, known_keys)
- Simplify import_from_local and build_local_file_data
- Rewrite all OMO service tests

Frontend:
- Delete OmoCommonConfigEditor.tsx and OmoGlobalConfigFields.tsx
- Delete src/lib/api/config.ts
- Remove OmoGlobalConfig type and merge preview functions
- Remove useGlobalConfig/useSaveGlobalConfig query hooks
- Simplify useOmoDraftState (remove all common config state)
- Replace OmoCommonConfigEditor with read-only JsonEditor preview
- Clean i18n keys (zh/en/ja)

src/lib/api/config.ts

@@ -1,28 +0,0 @@
-// 配置相关 API
-import { invoke } from "@tauri-apps/api/core";
-
-export type AppType = "claude" | "codex" | "gemini" | "omo" | "omo_slim";
-
-/**
- * 获取通用配置片段（统一接口）
- * @param appType - 应用类型（claude/codex/gemini）
- * @returns 通用配置片段（原始字符串），如果不存在则返回 null
- */
-export async function getCommonConfigSnippet(
-  appType: AppType,
-): Promise<string | null> {
-  return invoke<string | null>("get_common_config_snippet", { appType });
-}
-
-/**
- * 设置通用配置片段（统一接口）
- * @param appType - 应用类型（claude/codex/gemini）
- * @param snippet - 通用配置片段（原始字符串）
- * @throws 如果格式无效（Claude/Gemini 验证 JSON，Codex 暂不验证）
- */
-export async function setCommonConfigSnippet(
-  appType: AppType,
-  snippet: string,
-): Promise<void> {
-  return invoke("set_common_config_snippet", { appType, snippet });
-}

src/lib/api/index.ts

@@ -11,6 +11,5 @@ export { proxyApi } from "./proxy";
 export { openclawApi } from "./openclaw";
 export { sessionsApi } from "./sessions";
 export { workspaceApi } from "./workspace";
-export * as configApi from "./config";
 export type { ProviderSwitchEvent } from "./providers";
 export type { Prompt } from "./prompts";