[6/8] Add high-level Python SDK approval mode (#21910)

## Why

The high-level SDK should expose the approval behavior it actually
supports instead of leaking generated app-server routing fields. New
work should have two clear choices: default auto review, or explicitly
deny escalated permission requests. Existing threads and subsequent
turns should preserve their current approval behavior unless the caller
passes an override.

## What

- Add the public `ApprovalMode` enum with `auto_review` and `deny_all`.
- Default new thread creation to `ApprovalMode.auto_review`.
- Preserve existing approval settings by default for resume, fork, run,
and turn helpers.
- Remove raw `approval_policy` / `approvals_reviewer` kwargs from
high-level SDK wrappers.
- Update generated wrapper output, docs, examples, notebooks, and tests
for the high-level approval mode API.

## Stack

1. #21891 `[1/8]` Pin Python SDK runtime dependency
2. #21893 `[2/8]` Generate Python SDK types from pinned runtime
3. #21895 `[3/8]` Run Python SDK tests in CI
4. #21896 `[4/8]` Define Python SDK public API surface
5. #21905 `[5/8]` Rename Python SDK package to `openai-codex`
6. This PR `[6/8]` Add high-level Python SDK approval mode
7. #22014 `[7/8]` Add Python SDK app-server integration harness
8. #22021 `[8/8]` Add Python SDK Ruff formatting

## Verification

- Added approval-mode mapping/default tests for new threads, existing
threads, forks, resumes, and subsequent turns.

---------

Co-authored-by: Codex <noreply@openai.com>

sdk/python/src/openai_codex/__init__.py

@@ -14,6 +14,7 @@ from .errors import (
     is_retryable_error,
 )
 from .api import (
+    ApprovalMode,
     AsyncCodex,
     AsyncThread,
     AsyncTurnHandle,
@@ -37,6 +38,7 @@ __all__ = [
     "AppServerConfig",
     "Codex",
     "AsyncCodex",
+    "ApprovalMode",
     "Thread",
     "AsyncThread",
     "TurnHandle",