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-tauri/src/commands/config.rs

@@ -7,7 +7,6 @@ use tauri_plugin_opener::OpenerExt;
 use crate::app_config::AppType;
 use crate::codex_config;
 use crate::config::{self, get_claude_settings_path, ConfigStatus};
-use crate::settings;
 
 #[tauri::command]
 pub async fn get_claude_config_status() -> Result<ConfigStatus, String> {
@@ -16,18 +15,6 @@ pub async fn get_claude_config_status() -> Result<ConfigStatus, String> {
 
 use std::str::FromStr;
 
-fn invalid_json_format_error(error: serde_json::Error) -> String {
-    let lang = settings::get_settings()
-        .language
-        .unwrap_or_else(|| "zh".to_string());
-
-    match lang.as_str() {
-        "en" => format!("Invalid JSON format: {error}"),
-        "ja" => format!("JSON形式が無効です: {error}"),
-        _ => format!("无效的 JSON 格式: {error}"),
-    }
-}
-
 #[tauri::command]
 pub async fn get_config_status(app: String) -> Result<ConfigStatus, String> {
     match AppType::from_str(&app).map_err(|e| e.to_string())? {
@@ -163,71 +150,3 @@ pub async fn open_app_config_folder(handle: AppHandle) -> Result<bool, String> {
 
     Ok(true)
 }
-
-#[tauri::command]
-pub async fn get_common_config_snippet(
-    app_type: String,
-    state: tauri::State<'_, crate::store::AppState>,
-) -> Result<Option<String>, String> {
-    state
-        .db
-        .get_config_snippet(&app_type)
-        .map_err(|e| e.to_string())
-}
-
-#[tauri::command]
-pub async fn set_common_config_snippet(
-    app_type: String,
-    snippet: String,
-    state: tauri::State<'_, crate::store::AppState>,
-) -> Result<(), String> {
-    if !snippet.trim().is_empty() {
-        match app_type.as_str() {
-            "claude" | "gemini" | "omo" | "omo-slim" => {
-                serde_json::from_str::<serde_json::Value>(&snippet)
-                    .map_err(invalid_json_format_error)?;
-            }
-            "codex" => {}
-            _ => {}
-        }
-    }
-
-    let value = if snippet.trim().is_empty() {
-        None
-    } else {
-        Some(snippet)
-    };
-
-    state
-        .db
-        .set_config_snippet(&app_type, value)
-        .map_err(|e| e.to_string())?;
-
-    if app_type == "omo"
-        && state
-            .db
-            .get_current_omo_provider("opencode", "omo")
-            .map_err(|e| e.to_string())?
-            .is_some()
-    {
-        crate::services::OmoService::write_config_to_file(
-            state.inner(),
-            &crate::services::omo::STANDARD,
-        )
-        .map_err(|e| e.to_string())?;
-    }
-    if app_type == "omo-slim"
-        && state
-            .db
-            .get_current_omo_provider("opencode", "omo-slim")
-            .map_err(|e| e.to_string())?
-            .is_some()
-    {
-        crate::services::OmoService::write_config_to_file(
-            state.inner(),
-            &crate::services::omo::SLIM,
-        )
-        .map_err(|e| e.to_string())?;
-    }
-    Ok(())
-}