Enable git attribution across Codex entry points (#34819)

## What changed

- Install the git attribution extension in the app server, MCP server, and `codex debug prompt-input` so authenticated workspace policy controls the commit and pull request attribution instructions sent to the model.
- Resolve attribution settings from the process-level ChatGPT base URL, independent of per-thread or per-tool configuration overrides.
- Treat git attribution as contextual developer content when mapping model events.

## Testing

- Cover policy fetch retries, workspace switches, rollbacks, cold thread resumes with legacy instructions, MCP tool calls, and prompt-debug output.

GitOrigin-RevId: 57d182c432c20d7c1c6c429057b6163c9f32088d

codex-rs/mcp-server/src/message_processor.rs

@@ -67,6 +67,12 @@ impl MessageProcessor {
             config.codex_home.clone(),
         ));
         let mut extensions = ExtensionRegistryBuilder::<Config>::new();
+        codex_git_attribution::install(
+            &mut extensions,
+            auth_manager.clone(),
+            config.chatgpt_base_url.clone(),
+            config.http_client_factory(),
+        );
         codex_image_generation_extension::install(
             &mut extensions,
             auth_manager.clone(),