fix(codex): drop Python 3.11 requirement, auto-install python3

- tomllib fallback: try tomllib (3.11+) -> tomli -> minimal parser
- Works with Python 3.8+ (Ubuntu 20.04, Debian 11, etc.)
- Auto-install python3 if not found (like Gemini/Qwen scripts)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

codex/updater/config_validator.py

@@ -5,7 +5,42 @@ checks config.toml values and environment variables.
 """
 
 import os
-import tomllib
+try:
+    import tomllib
+except ModuleNotFoundError:
+    try:
+        import tomli as tomllib
+    except ModuleNotFoundError:
+        import re as _re
+        class _T:
+            @staticmethod
+            def load(f):
+                raw = f.read()
+                return _T._parse(raw.decode("utf-8") if isinstance(raw, bytes) else raw)
+            @staticmethod
+            def _parse(text):
+                result, cur = {}, None
+                for line in text.split("\n"):
+                    line = line.strip()
+                    if not line or line.startswith("#"):
+                        continue
+                    m = _re.match(r'^\[([^\]]+)\]$', line)
+                    if m:
+                        keys = [k.strip() for k in m.group(1).split(".")]
+                        cur = result
+                        for k in keys:
+                            cur = cur.setdefault(k, {})
+                        continue
+                    m = _re.match(r'^([^=]+?)\s*=\s*(.+)$', line)
+                    if m:
+                        k, v = m.group(1).strip(), m.group(2).strip()
+                        if v.startswith('"') and v.endswith('"'): v = v[1:-1]
+                        elif v == "true": v = True
+                        elif v == "false": v = False
+                        elif _re.match(r'^-?\d+$', v): v = int(v)
+                        (cur if cur is not None else result)[k] = v
+                return result
+        tomllib = _T()
 from dataclasses import dataclass
 from typing import Callable, Optional