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/providers/mod.rs

@@ -15,6 +15,8 @@ mod adapter;
 mod auth;
 mod claude;
 mod codex;
+pub(crate) mod codex_chat_common;
+pub mod codex_chat_history;
 pub mod codex_oauth_auth;
 pub mod copilot_auth;
 pub mod copilot_model_map;
@@ -42,8 +44,12 @@ pub use claude::{
     claude_api_format_needs_transform, get_claude_api_format,
     transform_claude_request_for_api_format, ClaudeAdapter,
 };
-pub use codex::should_convert_codex_responses_to_chat;
 pub use codex::CodexAdapter;
+pub use codex::{
+    apply_codex_chat_upstream_model, codex_provider_upstream_model,
+    codex_provider_uses_chat_completions, should_convert_codex_responses_to_chat,
+    CODEX_CHAT_CLIENT_MODEL,
+};
 pub use gemini::GeminiAdapter;
 
 /// 供应商类型枚举