feat: apply common config as runtime overlay instead of materialized merge

Common config snippets are now dynamically overlaid when writing live
files, rather than being pre-merged into provider snapshots at edit time.
This ensures that updating a snippet immediately takes effect for the
current provider and automatically propagates to other providers on
their next switch.

Key changes:
- Add write_live_with_common_config() overlay pipeline
- Strip common config from live before backfilling provider snapshots
- Normalize provider snapshots on save to keep them snippet-free
- Add explicit commonConfigEnabled flag in ProviderMeta (Option<bool>)
- Migrate legacy providers on snippet save (infer flag from subset check)
- Add Codex TOML snippet validation in set_common_config_snippet
- Stabilize onConfigChange callbacks with useCallback in ProviderForm

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_snapshot;
+use crate::services::provider::write_live_with_common_config;
 use serde_json::{json, Value};
 use std::str::FromStr;
 use std::sync::Arc;
@@ -1266,7 +1266,7 @@ impl ProxyService {
             return Ok(false);
         };
 
-        write_live_snapshot(app_type, provider)
+        write_live_with_common_config(self.db.as_ref(), app_type, provider)
             .map_err(|e| format!("写入 {app_type:?} Live 配置失败: {e}"))?;
 
         Ok(true)