feat: Phase 4 backend hardening — container reliability + security audit

Container Management (CONT-01 through CONT-06):
- Fix needs_archy_net: add lnd, nbxplorer to archy-net list
- Add StartupTier dependency ordering to health monitor (DB→Core→Dependent→App→UI)
- Add exponential backoff (10s/30s/90s) with 1hr stability reset
- Add get_health_check_args() with health checks for 20+ apps
- Add get_memory_limit() with per-app limits (128m-4g vs blanket 2g)
- Create docs/network-topology.md
- Fix fedimint containers on both nodes (moved to archy-net)

Security Audit (SEC-01 through SEC-06):
- Add sanitize_error_message() — strips internal paths from RPC errors
- Add validate_identity_id() — blocks path traversal on identity operations
- Add validate_did() — blocks path traversal on federation operations
- Add message size limits: node-send-message (1MB), dwn.write-message (10MB)
- Add rate limits for federation endpoints (join: 5/60s, invite: 10/300s)
- Configure journald (500MB max, 7 day retention) on both nodes
- Add /etc/logrotate.d/archipelago for backend + crowdsec logs
- Verify all 4 nginx security headers on both nodes

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

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

@@ -151,6 +151,14 @@ impl RpcHandler {
         let data_format = params["dataFormat"].as_str();
         let data = params.get("data").cloned();
 
+        // Limit data size to 10MB to prevent disk exhaustion
+        if let Some(ref d) = data {
+            let data_str = d.to_string();
+            if data_str.len() > 10_485_760 {
+                anyhow::bail!("Message data too large (max 10MB)");
+            }
+        }
+
         let store = DwnStore::new(&self.config.data_dir).await?;
         let message = store
             .write_message(author, protocol, schema, data_format, data)