feat: add webhook notification system with Settings UI (REMOTE-03)

Webhook module with HTTP delivery, HMAC-SHA256 signing, and event
filtering. RPC handlers for get-config, configure, and test endpoints.
Settings page gains webhook configuration section with URL, secret,
event toggles, and test button.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

core/archipelago/src/api/rpc/mod.rs

@@ -26,6 +26,7 @@ mod system;
 mod update;
 mod vpn;
 mod wallet;
+mod webhooks;
 
 use crate::auth::AuthManager;
 use crate::config::Config;
@@ -490,6 +491,11 @@ impl RpcHandler {
                 self.handle_security_list_expiring(&p).await
             }
 
+            // Webhooks
+            "webhook.get-config" => self.handle_webhook_get_config().await,
+            "webhook.configure" => self.handle_webhook_configure(params).await,
+            "webhook.test" => self.handle_webhook_test().await,
+
             _ => {
                 Err(anyhow::anyhow!("Unknown method: {}", rpc_req.method))
             }

core/archipelago/src/api/rpc/webhooks.rs

@@ -0,0 +1,83 @@
+use super::RpcHandler;
+use crate::webhooks;
+use anyhow::Result;
+use tracing::info;
+
+impl RpcHandler {
+    /// webhook.get-config — Get current webhook configuration.
+    pub(super) async fn handle_webhook_get_config(&self) -> Result<serde_json::Value> {
+        let config = webhooks::load_config(&self.config.data_dir).await?;
+        Ok(serde_json::json!({
+            "enabled": config.enabled,
+            "url": config.url,
+            "events": config.events,
+            "has_secret": config.secret.is_some(),
+        }))
+    }
+
+    /// webhook.configure — Update webhook configuration.
+    pub(super) async fn handle_webhook_configure(
+        &self,
+        params: Option<serde_json::Value>,
+    ) -> Result<serde_json::Value> {
+        let params = params.ok_or_else(|| anyhow::anyhow!("Missing params"))?;
+
+        let mut config = webhooks::load_config(&self.config.data_dir).await?;
+
+        if let Some(enabled) = params.get("enabled").and_then(|v| v.as_bool()) {
+            config.enabled = enabled;
+        }
+        if let Some(url) = params.get("url").and_then(|v| v.as_str()) {
+            config.url = url.to_string();
+        }
+        if let Some(secret) = params.get("secret").and_then(|v| v.as_str()) {
+            config.secret = if secret.is_empty() {
+                None
+            } else {
+                Some(secret.to_string())
+            };
+        }
+        if let Some(events) = params.get("events") {
+            if let Ok(parsed) = serde_json::from_value::<Vec<webhooks::WebhookEvent>>(events.clone())
+            {
+                config.events = parsed;
+            }
+        }
+
+        webhooks::save_config(&self.config.data_dir, &config).await?;
+        info!("Webhook config updated: enabled={}, url={}", config.enabled, config.url);
+
+        Ok(serde_json::json!({
+            "configured": true,
+            "enabled": config.enabled,
+            "url": config.url,
+        }))
+    }
+
+    /// webhook.test — Send a test webhook notification.
+    pub(super) async fn handle_webhook_test(&self) -> Result<serde_json::Value> {
+        let config = webhooks::load_config(&self.config.data_dir).await?;
+        if !config.enabled || config.url.is_empty() {
+            anyhow::bail!("Webhook is not configured. Set a URL and enable it first.");
+        }
+
+        let payload = webhooks::WebhookPayload {
+            event: webhooks::WebhookEvent::ContainerCrash,
+            title: "Test Notification".to_string(),
+            message: "This is a test webhook from your Archipelago node.".to_string(),
+            timestamp: chrono::Utc::now().to_rfc3339(),
+            node_id: {
+                let (data, _) = self.state_manager.get_snapshot().await;
+                data.server_info.id
+            },
+            details: Some(serde_json::json!({"test": true})),
+        };
+
+        webhooks::send_webhook(&self.config.data_dir, payload).await;
+
+        Ok(serde_json::json!({
+            "sent": true,
+            "url": config.url,
+        }))
+    }
+}