fix: implement 22 security pentest remediation fixes

Server-side session management with SHA-256 hashed tokens and HttpOnly
cookies. Auth middleware gating all RPC/WS/proxy routes with method
allowlist. Login rate limiting (5/60s per IP). CORS restricted to
config origin. Docker registry allowlist. App ID and path validation.
P2P message sanitization (HTML + log injection). Onion address and
known-peer validation. Nginx security headers (CSP, X-Frame-Options,
etc.) and AIUI proxy auth. Systemd hardening (non-root, NoNewPrivileges,
ProtectSystem).

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

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

@@ -60,6 +60,19 @@ impl RpcHandler {
             .get("message")
             .and_then(|v| v.as_str())
             .ok_or_else(|| anyhow::anyhow!("Missing message"))?;
+
+        // Validate onion is a known peer to prevent SSRF to arbitrary Tor destinations
+        let known_peers = peers::load_peers(&self.config.data_dir).await?;
+        let is_known = known_peers.iter().any(|p| {
+            p.onion == onion || p.onion == format!("{}.onion", onion)
+                || format!("{}.onion", p.onion) == onion
+        });
+        if !is_known {
+            return Err(anyhow::anyhow!(
+                "Onion address not in known peers list. Add the peer first."
+            ));
+        }
+
         let (data, _) = self.state_manager.get_snapshot().await;
         let pubkey = data.server_info.pubkey.clone();
         node_message::send_to_peer(onion, &pubkey, message).await?;