revert: restore full config overwrite + Common Config Snippet (revert 992dda5c)

Revert the partial key-field merging refactoring introduced in 992dda5c,
along with two dependent commits (24fa8a18, 87604b18) that referenced
the now-removed ClaudeQuickToggles component.

The whitelist-based partial merge approach had critical issues:
- Non-whitelisted custom fields were lost during provider switching
- Backfill permanently stripped non-key fields from the database
- Whitelist required constant maintenance to track upstream changes

This restores the proven "full config overwrite + Common Config Snippet"
architecture where each provider stores its complete configuration and
shared settings are managed via a separate snippet mechanism.

Reverted commits:
- 24fa8a18: context-aware JSON editor hint + hide quick toggles
- 87604b18: hide ClaudeQuickToggles when creating
- 992dda5c: partial key-field merging refactoring

Restored:
- Full config snapshot write (write_live_snapshot) for Claude/Codex/Gemini
- Full config backfill (settings_config = live_config)
- Common Config Snippet UI and backend commands
- 6 frontend components/hooks for common config editing
- configApi barrel export and DB snippet methods

Removed:
- ClaudeQuickToggles component
- write_live_partial / backfill_key_fields / patch_claude_live
- All KEY_FIELDS constants

src-tauri/src/app_config.rs

@@ -352,6 +352,49 @@ impl FromStr for AppType {
     }
 }
 
+/// 通用配置片段（按应用分治）
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
+pub struct CommonConfigSnippets {
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub claude: Option<String>,
+
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub codex: Option<String>,
+
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub gemini: Option<String>,
+
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub opencode: Option<String>,
+
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub openclaw: Option<String>,
+}
+
+impl CommonConfigSnippets {
+    /// 获取指定应用的通用配置片段
+    pub fn get(&self, app: &AppType) -> Option<&String> {
+        match app {
+            AppType::Claude => self.claude.as_ref(),
+            AppType::Codex => self.codex.as_ref(),
+            AppType::Gemini => self.gemini.as_ref(),
+            AppType::OpenCode => self.opencode.as_ref(),
+            AppType::OpenClaw => self.openclaw.as_ref(),
+        }
+    }
+
+    /// 设置指定应用的通用配置片段
+    pub fn set(&mut self, app: &AppType, snippet: Option<String>) {
+        match app {
+            AppType::Claude => self.claude = snippet,
+            AppType::Codex => self.codex = snippet,
+            AppType::Gemini => self.gemini = snippet,
+            AppType::OpenCode => self.opencode = snippet,
+            AppType::OpenClaw => self.openclaw = snippet,
+        }
+    }
+}
+
 /// 多应用配置结构（向后兼容）
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct MultiAppConfig {
@@ -369,6 +412,12 @@ pub struct MultiAppConfig {
     /// Claude Skills 配置
     #[serde(default)]
     pub skills: SkillStore,
+    /// 通用配置片段（按应用分治）
+    #[serde(default)]
+    pub common_config_snippets: CommonConfigSnippets,
+    /// Claude 通用配置片段（旧字段，用于向后兼容迁移）
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub claude_common_config_snippet: Option<String>,
 }
 
 fn default_version() -> u32 {
@@ -390,6 +439,8 @@ impl Default for MultiAppConfig {
             mcp: McpRoot::default(),
             prompts: PromptRoot::default(),
             skills: SkillStore::default(),
+            common_config_snippets: CommonConfigSnippets::default(),
+            claude_common_config_snippet: None,
         }
     }
 }
@@ -483,6 +534,15 @@ impl MultiAppConfig {
             updated = true;
         }
 
+        // 迁移通用配置片段：claude_common_config_snippet → common_config_snippets.claude
+        if let Some(old_claude_snippet) = config.claude_common_config_snippet.take() {
+            log::info!(
+                "迁移通用配置：claude_common_config_snippet → common_config_snippets.claude"
+            );
+            config.common_config_snippets.claude = Some(old_claude_snippet);
+            updated = true;
+        }
+
         if updated {
             log::info!("配置结构已更新（包括 MCP 迁移或 Prompt 自动导入），保存配置...");
             config.save()?;