Add Chat Completions routing for Codex providers

- Add a Codex API format selector and routing badge for Chat Completions providers.
- Convert Codex Responses requests to upstream Chat Completions when routing is required.
- Convert Chat Completions JSON and SSE responses back to Responses format.
- Keep generated Codex wire_api values on Responses for Codex compatibility.
- Add i18n labels, provider metadata handling, and focused conversion tests.

src-tauri/src/proxy/handler_config.rs

@@ -47,7 +47,7 @@ fn openai_stream_usage_event_filter(data: &str) -> bool {
     data.contains("\"usage\"")
 }
 
-fn codex_stream_usage_event_filter(data: &str) -> bool {
+pub fn codex_stream_usage_event_filter(data: &str) -> bool {
     data.contains("\"response.completed\"") || data.contains("\"usage\"")
 }