feat(setup): add Codex CLI setup recipe (#1243)

* Add Codex setup recipe

* Sync beads issues (bd-1zo)

---------

Co-authored-by: Amp <amp@example.com>

cmd/bd/setup/codex.go

@@ -0,0 +1,45 @@
+package setup
+
+var codexIntegration = agentsIntegration{
+	name:         "Codex CLI",
+	setupCommand: "bd setup codex",
+	readHint:     "Codex reads AGENTS.md at the start of each run or session. Restart Codex if it is already running.",
+}
+
+var codexEnvProvider = defaultAgentsEnv
+
+// InstallCodex installs Codex integration.
+func InstallCodex() {
+	env := codexEnvProvider()
+	if err := installCodex(env); err != nil {
+		setupExit(1)
+	}
+}
+
+func installCodex(env agentsEnv) error {
+	return installAgents(env, codexIntegration)
+}
+
+// CheckCodex checks if Codex integration is installed.
+func CheckCodex() {
+	env := codexEnvProvider()
+	if err := checkCodex(env); err != nil {
+		setupExit(1)
+	}
+}
+
+func checkCodex(env agentsEnv) error {
+	return checkAgents(env, codexIntegration)
+}
+
+// RemoveCodex removes Codex integration.
+func RemoveCodex() {
+	env := codexEnvProvider()
+	if err := removeCodex(env); err != nil {
+		setupExit(1)
+	}
+}
+
+func removeCodex(env agentsEnv) error {
+	return removeAgents(env, codexIntegration)
+}