Add Python SDK public API and examples (#14446)

## TL;DR
WIP esp the examples

Thin the Python SDK public surface so the wrapper layer returns
canonical app-server generated models directly.

- keeps `Codex` / `AsyncCodex` / `Thread` / `Turn` and input helpers,
but removes alias-only type layers and custom result models
- `metadata` now returns `InitializeResponse` and `run()` returns the
generated app-server `Turn`
- updates docs, examples, notebook, and tests to use canonical generated
types and regenerates `v2_all.py` against current schema
- keeps the pinned runtime-package integration flow and real integration
coverage

  ## Validation
  - `PYTHONPATH=sdk/python/src python3 -m pytest sdk/python/tests`
- `GH_TOKEN="$(gh auth token)" RUN_REAL_CODEX_TESTS=1
PYTHONPATH=sdk/python/src python3 -m pytest sdk/python/tests -rs`

---------

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

sdk/python/examples/01_quickstart_constructor/sync.py

@@ -0,0 +1,28 @@
+import sys
+from pathlib import Path
+
+_EXAMPLES_ROOT = Path(__file__).resolve().parents[1]
+if str(_EXAMPLES_ROOT) not in sys.path:
+    sys.path.insert(0, str(_EXAMPLES_ROOT))
+
+from _bootstrap import (
+    assistant_text_from_turn,
+    ensure_local_sdk_src,
+    find_turn_by_id,
+    runtime_config,
+    server_label,
+)
+
+ensure_local_sdk_src()
+
+from codex_app_server import Codex, TextInput
+
+with Codex(config=runtime_config()) as codex:
+    print("Server:", server_label(codex.metadata))
+
+    thread = codex.thread_start(model="gpt-5.4", config={"model_reasoning_effort": "high"})
+    result = thread.turn(TextInput("Say hello in one sentence.")).run()
+    persisted = thread.read(include_turns=True)
+    persisted_turn = find_turn_by_id(persisted.thread.turns, result.id)
+    print("Status:", result.status)
+    print("Text:", assistant_text_from_turn(persisted_turn))