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/ucodex_install.sh

@@ -37,21 +37,34 @@ echo -e "${NC}"
 
 # ---- Check prerequisites ----
 
-for cmd in python3 curl tar; do
+install_pkg() {
+    if command -v apt-get >/dev/null 2>&1; then
+        apt-get update -qq && apt-get install -y -qq "$@"
+    elif command -v dnf >/dev/null 2>&1; then
+        dnf install -y -q "$@"
+    elif command -v yum >/dev/null 2>&1; then
+        yum install -y -q "$@"
+    elif command -v brew >/dev/null 2>&1; then
+        brew install "$@"
+    else
+        err "No package manager found. Install $* manually."
+        return 1
+    fi
+}
+
+if ! command -v python3 &>/dev/null; then
+    info "python3 not found, installing..."
+    install_pkg python3
+fi
+
+for cmd in curl tar; do
     if ! command -v "$cmd" &>/dev/null; then
         err "$cmd is required but not found"
         exit 1
     fi
 done
 
-PY_VER=$(python3 -c "import sys; print(f'{sys.version_info.major}.{sys.version_info.minor}')")
-PY_MAJOR=$(echo "$PY_VER" | cut -d. -f1)
-PY_MINOR=$(echo "$PY_VER" | cut -d. -f2)
-if [ "$PY_MAJOR" -lt 3 ] || ([ "$PY_MAJOR" -eq 3 ] && [ "$PY_MINOR" -lt 11 ]); then
-    err "Python 3.11+ required (found $PY_VER)"
-    exit 1
-fi
-log "Python3 $PY_VER"
+log "Python3 $(python3 --version | awk '{print $2}')"
 
 # ---- Step 1: Install Codex binary from GitHub ----