refactor(provider): switch from full config overwrite to partial key-field merging

Replace the provider switching mechanism for Claude/Codex/Gemini from
full settings_config overwrite to partial key-field replacement, preserving
user's non-provider settings (plugins, MCP, permissions, etc.) across switches.

- Add write_live_partial() with per-app implementations for Claude (JSON env
  merge), Codex (auth replace + TOML partial merge), and Gemini (env merge)
- Add backfill_key_fields() to extract only provider-specific fields when
  saving live config back to provider entries
- Update switch_normal, sync_current_to_live, add, update to use partial merge
- Remove common config snippet feature for Claude/Codex/Gemini (no longer
  needed with partial merging); preserve OMO common config
- Delete 6 frontend files (3 components + 3 hooks), clean up 11 modified files
- Remove backend extract_common_config_* methods, 3 Tauri commands,
  CommonConfigSnippets struct, and related migration code
- Update integration tests to validate key-field-only backfill behavior

src/components/providers/forms/CodexConfigEditor.tsx

@@ -1,6 +1,5 @@
-import React, { useState, useEffect } from "react";
+import React from "react";
 import { CodexAuthSection, CodexConfigSection } from "./CodexConfigSections";
-import { CodexCommonConfigModal } from "./CodexCommonConfigModal";
 
 interface CodexConfigEditorProps {
   authValue: string;
@@ -13,23 +12,9 @@ interface CodexConfigEditorProps {
 
   onAuthBlur?: () => void;
 
-  useCommonConfig: boolean;
-
-  onCommonConfigToggle: (checked: boolean) => void;
-
-  commonConfigSnippet: string;
-
-  onCommonConfigSnippetChange: (value: string) => void;
-
-  commonConfigError: string;
-
   authError: string;
 
-  configError: string; // config.toml 错误提示
-
-  onExtract?: () => void;
-
-  isExtracting?: boolean;
+  configError: string;
 }
 
 const CodexConfigEditor: React.FC<CodexConfigEditorProps> = ({
@@ -38,25 +23,9 @@ const CodexConfigEditor: React.FC<CodexConfigEditorProps> = ({
   onAuthChange,
   onConfigChange,
   onAuthBlur,
-  useCommonConfig,
-  onCommonConfigToggle,
-  commonConfigSnippet,
-  onCommonConfigSnippetChange,
-  commonConfigError,
   authError,
   configError,
-  onExtract,
-  isExtracting,
 }) => {
-  const [isCommonConfigModalOpen, setIsCommonConfigModalOpen] = useState(false);
-
-  // Auto-open common config modal if there's an error
-  useEffect(() => {
-    if (commonConfigError && !isCommonConfigModalOpen) {
-      setIsCommonConfigModalOpen(true);
-    }
-  }, [commonConfigError, isCommonConfigModalOpen]);
-
   return (
     <div className="space-y-6">
       {/* Auth JSON Section */}
@@ -71,23 +40,8 @@ const CodexConfigEditor: React.FC<CodexConfigEditorProps> = ({
       <CodexConfigSection
         value={configValue}
         onChange={onConfigChange}
-        useCommonConfig={useCommonConfig}
-        onCommonConfigToggle={onCommonConfigToggle}
-        onEditCommonConfig={() => setIsCommonConfigModalOpen(true)}
-        commonConfigError={commonConfigError}
         configError={configError}
       />
-
-      {/* Common Config Modal */}
-      <CodexCommonConfigModal
-        isOpen={isCommonConfigModalOpen}
-        onClose={() => setIsCommonConfigModalOpen(false)}
-        value={commonConfigSnippet}
-        onChange={onCommonConfigSnippetChange}
-        error={commonConfigError}
-        onExtract={onExtract}
-        isExtracting={isExtracting}
-      />
     </div>
   );
 };