Add enforce_residency to requirements (#10263)

Add `enforce_residency` to requirements.toml and thread it through to a
header on `default_client`.

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -497,6 +497,14 @@ pub struct ConfigReadResponse {
 pub struct ConfigRequirements {
     pub allowed_approval_policies: Option<Vec<AskForApproval>>,
     pub allowed_sandbox_modes: Option<Vec<SandboxMode>>,
+    pub enforce_residency: Option<ResidencyRequirement>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "lowercase")]
+#[ts(export_to = "v2/")]
+pub enum ResidencyRequirement {
+    Us,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]