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/types/omo.ts

@@ -1,25 +1,7 @@
-export interface OmoGlobalConfig {
-  id: string;
-  schemaUrl?: string;
-  sisyphusAgent?: Record<string, unknown>;
-  disabledAgents: string[];
-  disabledMcps: string[];
-  disabledHooks: string[];
-  disabledSkills: string[];
-  lsp?: Record<string, unknown>;
-  experimental?: Record<string, unknown>;
-  backgroundTask?: Record<string, unknown>;
-  browserAutomationEngine?: Record<string, unknown>;
-  claudeCode?: Record<string, unknown>;
-  otherFields?: Record<string, unknown>;
-  updatedAt: string;
-}
-
 export interface OmoLocalFileData {
   agents?: Record<string, Record<string, unknown>>;
   categories?: Record<string, Record<string, unknown>>;
   otherFields?: Record<string, unknown>;
-  global: OmoGlobalConfig;
   filePath: string;
   lastModified?: string;
 }
@@ -406,75 +388,6 @@ export const OMO_SLIM_DISABLEABLE_HOOKS = [
 export const OMO_SLIM_DEFAULT_SCHEMA_URL =
   "https://raw.githubusercontent.com/alvinunreal/oh-my-opencode-slim/master/assets/oh-my-opencode-slim.schema.json";
 
-export function mergeOmoConfigPreview(
-  global: OmoGlobalConfig | undefined,
-  agents: Record<string, Record<string, unknown>>,
-  categories: Record<string, Record<string, unknown>> | undefined,
-  otherFieldsStr: string,
-  options?: { slim?: boolean },
-): Record<string, unknown> {
-  const result: Record<string, unknown> = {};
-  const isSlim = options?.slim ?? false;
-
-  if (global) {
-    if (global.schemaUrl) result["$schema"] = global.schemaUrl;
-
-    if (!isSlim) {
-      if (global.sisyphusAgent) result["sisyphus_agent"] = global.sisyphusAgent;
-    }
-    if (global.disabledAgents?.length)
-      result["disabled_agents"] = global.disabledAgents;
-    if (global.disabledMcps?.length)
-      result["disabled_mcps"] = global.disabledMcps;
-    if (global.disabledHooks?.length)
-      result["disabled_hooks"] = global.disabledHooks;
-
-    if (!isSlim) {
-      if (global.disabledSkills?.length)
-        result["disabled_skills"] = global.disabledSkills;
-      if (global.lsp) result["lsp"] = global.lsp;
-      if (global.experimental) result["experimental"] = global.experimental;
-      if (global.backgroundTask)
-        result["background_task"] = global.backgroundTask;
-      if (global.browserAutomationEngine)
-        result["browser_automation_engine"] = global.browserAutomationEngine;
-      if (global.claudeCode) result["claude_code"] = global.claudeCode;
-    }
-
-    if (global.otherFields) {
-      for (const [k, v] of Object.entries(global.otherFields)) {
-        result[k] = v;
-      }
-    }
-  }
-
-  if (Object.keys(agents).length > 0) result["agents"] = agents;
-  if (!isSlim && categories && Object.keys(categories).length > 0)
-    result["categories"] = categories;
-
-  try {
-    const other = parseOmoOtherFieldsObject(otherFieldsStr);
-    if (other) {
-      for (const [k, v] of Object.entries(other)) {
-        result[k] = v;
-      }
-    }
-  } catch {}
-
-  return result;
-}
-
-/** @deprecated Use mergeOmoConfigPreview with options.slim=true */
-export function mergeOmoSlimConfigPreview(
-  global: OmoGlobalConfig | undefined,
-  agents: Record<string, Record<string, unknown>>,
-  otherFieldsStr: string,
-): Record<string, unknown> {
-  return mergeOmoConfigPreview(global, agents, undefined, otherFieldsStr, {
-    slim: true,
-  });
-}
-
 export function buildOmoProfilePreview(
   agents: Record<string, Record<string, unknown>>,
   categories: Record<string, Record<string, unknown>> | undefined,