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/services/proxy.rs

@@ -8,7 +8,7 @@ use crate::database::Database;
 use crate::provider::Provider;
 use crate::proxy::server::ProxyServer;
 use crate::proxy::types::*;
-use crate::services::provider::write_live_partial;
+use crate::services::provider::write_live_snapshot;
 use serde_json::{json, Value};
 use std::str::FromStr;
 use std::sync::Arc;
@@ -1266,7 +1266,7 @@ impl ProxyService {
             return Ok(false);
         };
 
-        write_live_partial(app_type, provider)
+        write_live_snapshot(app_type, provider)
             .map_err(|e| format!("写入 {app_type:?} Live 配置失败: {e}"))?;
 
         Ok(true)