Add Codex research skills and setup docs

Include Codex setup docs, installer updates, and switch the OpenCode web research agent default model to gpt-5.4.

scripts/install-codex.sh

@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+CODEX_HOME="${CODEX_HOME:-$HOME/.codex}"
+CONFIG_PATH="$CODEX_HOME/config.toml"
+
+mkdir -p "$CODEX_HOME"
+
+python3 - "$CONFIG_PATH" <<'PY'
+import re
+import sys
+from pathlib import Path
+
+config_path = Path(sys.argv[1])
+text = config_path.read_text(encoding="utf-8") if config_path.exists() else ""
+
+blocks = {
+    "features": """[features]
+multi_agent = true
+default_mode_request_user_input = true
+""",
+    "agents.web_researcher": """[agents.web_researcher]
+description = "Use this agent when you need to research information on the internet, particularly for debugging issues, finding solutions to technical problems, or gathering comprehensive information from multiple sources. This agent excels at finding relevant discussions. Use when you need creative search strategies, thorough investigation, or compilation of findings from multiple sources."
+config_file = "agents/web-researcher.toml"
+""",
+}
+
+for section, block in blocks.items():
+    pattern = rf"(?ms)^\[{re.escape(section)}\]\n.*?(?=^\[|\Z)"
+    if re.search(pattern, text):
+        text = re.sub(pattern, block, text)
+    else:
+        text = text.rstrip() + ("\n\n" if text.strip() else "") + block
+
+text = re.sub(r"(?m)^suppress_unstable_features_warning\s*=.*\n?", "", text).strip()
+text = 'suppress_unstable_features_warning = true\n\n' + text
+
+config_path.write_text(text.rstrip() + "\n", encoding="utf-8")
+PY
+
+echo "Updated Codex config at $CONFIG_PATH"