fix: add health RPC handler, Nostr connect timeouts, atomic backup restore, nginx rate limits

- R1: Add health RPC endpoint with crash recovery status, uptime, and version
- R2: Wrap all 5 Nostr client.connect() calls in 10s timeout
- R3: Make backup restore atomic with staging dir and rollback on failure
- I1: Add rate limiting, body size, and proxy timeouts to unauthenticated nginx endpoints

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/archipelago/src/api/handler.rs

@@ -147,8 +147,13 @@ impl ApiHandler {
 
             // Health — unauthenticated, returns JSON with service status
             (Method::GET, "/health") => {
+                let recovery_complete = crate::crash_recovery::is_recovery_complete();
+                let uptime = crate::crash_recovery::uptime_seconds();
+                let health_status = if recovery_complete { "ok" } else { "degraded" };
                 let status = serde_json::json!({
-                    "status": "ok",
+                    "status": health_status,
+                    "crash_recovery_complete": recovery_complete,
+                    "uptime_seconds": uptime,
                     "version": env!("CARGO_PKG_VERSION"),
                     "services": {
                         "rpc": true,

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

@@ -440,6 +440,7 @@ impl RpcHandler {
         let result = match rpc_req.method.as_str() {
             "echo" => self.handle_echo(params).await,
             "server.echo" => self.handle_echo(params).await,
+            "health" => self.handle_health().await,
             "auth.login" => self.handle_auth_login(params).await,
             "auth.logout" => self.handle_auth_logout().await,
             "auth.changePassword" => self.handle_auth_change_password(params, &session_token).await,
@@ -1040,6 +1041,18 @@ impl RpcHandler {
         }
         Ok(serde_json::json!({ "message": "Hello from Archipelago!" }))
     }
+
+    async fn handle_health(&self) -> Result<serde_json::Value> {
+        let recovery_complete = crate::crash_recovery::is_recovery_complete();
+        let uptime = crate::crash_recovery::uptime_seconds();
+        let status = if recovery_complete { "ok" } else { "degraded" };
+        Ok(serde_json::json!({
+            "status": status,
+            "crash_recovery_complete": recovery_complete,
+            "uptime_seconds": uptime,
+            "version": env!("CARGO_PKG_VERSION"),
+        }))
+    }
 }
 
 /// Derive a CSRF token from the session token via HMAC.