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/provider.rs

@@ -235,11 +235,6 @@ pub struct ProviderMeta {
     /// - "openai_chat": OpenAI Chat Completions 格式，需要转换
     #[serde(rename = "apiFormat", skip_serializing_if = "Option::is_none")]
     pub api_format: Option<String>,
-    /// Claude 认证字段名（仅 Claude 供应商使用）
-    /// - "ANTHROPIC_AUTH_TOKEN" (默认): 大多数第三方/聚合供应商
-    /// - "ANTHROPIC_API_KEY": 少数供应商需要原生 API Key
-    #[serde(rename = "apiKeyField", skip_serializing_if = "Option::is_none")]
-    pub api_key_field: Option<String>,
 }
 
 impl ProviderManager {