feat(m3-hermes): add Hermes Dashboard as systemd service with Netbird-only firewall

- New hermes-dashboard.service: runs 'hermes dashboard' on 0.0.0.0:9119
- Firewall restricts port 9119 to Netbird mesh VPN range (100.64.0.0/16)
- Runs as hermes user with NoNewPrivileges + ProtectSystem hardening
- Depends on hermes-agent.service (starts after gateway)
- Added placeholder hermes-api-server-key.age (needs real encryption on host)

hosts/m3-hermes/services/default.nix

@@ -1,6 +1,7 @@
 {
   imports = [
     ./hermes-agent.nix
+    ./hermes-dashboard.nix
     ./netbird.nix
   ];
 }

hosts/m3-hermes/services/hermes-dashboard.nix

@@ -0,0 +1,62 @@
+{
+  config,
+  pkgs,
+  inputs,
+  ...
+}: let
+  # Netbird mesh VPN range — dashboard only accessible from mesh peers
+  netbirdRange = "100.64.0.0/16";
+
+  # Reference the hermes-agent package from the running service config
+  hermesPkg = config.services.hermes-agent.package or (inputs.hermes-agent.packages.${pkgs.stdenv.hostPlatform.system}.default or pkgs.hermes-agent);
+in {
+  # ── Hermes Dashboard systemd service ───────────────────────────────────
+  # Web UI for managing Hermes Agent — sessions, config, kanban, cron, etc.
+  # Binds to 0.0.0.0:9119 but firewall restricts to Netbird mesh only.
+  systemd.services.hermes-dashboard = {
+    description = "Hermes Agent Web Dashboard";
+    after = ["network.target" "hermes-agent.service"];
+    wants = ["hermes-agent.service"];
+    wantedBy = ["multi-user.target"];
+
+    serviceConfig = {
+      Type = "simple";
+      User = "hermes";
+      Group = "hermes";
+
+      ExecStart = "${hermesPkg}/bin/hermes dashboard --host 0.0.0.0 --port 9119 --no-open";
+
+      # Environment matching the hermes-agent service
+      Environment = [
+        "HERMES_HOME=/var/lib/hermes/.hermes"
+        "HERMES_MANAGED=true"
+        "HOME=/var/lib/hermes"
+      ];
+
+      # Security hardening (matching hermes-agent service pattern)
+      NoNewPrivileges = true;
+      ProtectSystem = "strict";
+      ProtectHome = "read-only";
+      ReadWritePaths = ["/var/lib/hermes" "/tmp"];
+      PrivateTmp = true;
+
+      # Restart policy
+      Restart = "on-failure";
+      RestartSec = 5;
+    };
+  };
+
+  # ── Firewall: Dashboard only from Netbird mesh ─────────────────────────
+  networking.firewall = {
+    # Use extraCommands for source-IP-restricted port (NixOS firewall
+    # allowedTCPPorts is all-or-nothing per port).
+    extraCommands = ''
+      # Allow Hermes Dashboard (9119/tcp) only from Netbird mesh VPN
+      ip46tables -A nixos-fw -p tcp --dport 9119 -s ${netbirdRange} -j nixos-fw-accept
+    '';
+
+    extraStopCommands = ''
+      ip46tables -D nixos-fw -p tcp --dport 9119 -s ${netbirdRange} -j nixos-fw-accept 2>/dev/null || true
+    '';
+  };
+}