Handle expired agreements and rewrite README

- Implement robust End User Agreement expiry detection and handling
- Add graceful error recovery for failed accounts
- Rewrite README.md to focus on user benefits
- Add documentation guidelines to AGENTS.md

gocardless-client/src/models.rs

@@ -14,6 +14,16 @@ pub struct Requisition {
     pub status: String,
     pub accounts: Option<Vec<String>>,
     pub reference: Option<String>,
+    pub agreement: Option<String>, // EUA ID associated with this requisition
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct EndUserAgreement {
+    pub id: String,
+    pub created: Option<String>,
+    pub accepted: Option<String>, // When user accepted the agreement
+    pub access_valid_for_days: Option<i32>, // Validity period (default 90)
+    pub institution_id: Option<String>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]