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/app-server/Cargo.toml

@@ -47,6 +47,7 @@ codex-extension-api = { workspace = true }
 codex-external-agent-migration = { workspace = true }
 codex-features = { workspace = true }
 codex-goal-extension = { workspace = true }
+codex-git-attribution = { workspace = true }
 codex-guardian = { workspace = true }
 codex-git-utils = { workspace = true }
 codex-file-watcher = { workspace = true }