Add Codex Chat-to-Responses bridge

- Add Codex provider API format selection and model mapping for Chat-only upstreams.
- Convert Codex Responses requests to Chat Completions and rebuild Chat responses as Responses output.
- Preserve reasoning_content across non-streaming, streaming, tool calls, and previous_response_id follow-ups.
- Add a bounded Codex Chat history cache for restoring tool calls before tool outputs.
- Cover Chat bridge, compact routing, streaming, and history recovery with focused tests.

src-tauri/src/proxy/response_processor.rs

@@ -818,7 +818,9 @@ mod tests {
     use crate::provider::ProviderMeta;
     use crate::proxy::failover_switch::FailoverSwitchManager;
     use crate::proxy::provider_router::ProviderRouter;
-    use crate::proxy::providers::gemini_shadow::GeminiShadowStore;
+    use crate::proxy::providers::{
+        codex_chat_history::CodexChatHistoryStore, gemini_shadow::GeminiShadowStore,
+    };
     use crate::proxy::types::{ProxyConfig, ProxyStatus};
     use rust_decimal::Decimal;
     use std::collections::HashMap;
@@ -940,6 +942,7 @@ mod tests {
             current_providers: Arc::new(RwLock::new(HashMap::new())),
             provider_router: Arc::new(ProviderRouter::new(db.clone())),
             gemini_shadow: Arc::new(GeminiShadowStore::default()),
+            codex_chat_history: Arc::new(CodexChatHistoryStore::default()),
             app_handle: None,
             failover_manager: Arc::new(FailoverSwitchManager::new(db)),
         }