feat: add Feature Manager to Sovran Hub dashboard

- flake.nix: import /etc/nixos/hub-overrides.nix alongside custom.nix
- sovran-hub.nix: add hub-overrides-init service (seeds file if missing),
  sovran-hub-rebuild service (nixos-rebuild switch only), and
  feature_manager=true in generated config.json
- server.py: add FEATURE_REGISTRY with 6 features (rdp, haven,
  element-calling, mempool, bip110, bitcoin-core); add hub-overrides.nix
  read/write helpers; add /api/features, /api/features/toggle,
  /api/rebuild/status, /api/domains/set, /api/domains/set-email,
  /api/domains/status endpoints; update /api/config to expose feature_manager
- index.html: add domain setup modal, SSL email modal, feature confirm
  modal, and rebuild modal HTML
- app.js: add Feature Manager rendering with sub-category layout,
  feature toggle cards with sliding toggles, domain setup flow,
  SSL email collection, conflict confirmation, rebuild polling
- style.css: add Feature Manager styles (feature cards, toggle switch,
  domain badge, conflict warning, domain input fields)"

Agent-Logs-Url: https://github.com/naturallaw777/staging_alpha/sessions/9088415a-efc3-4dd1-9c22-877a543af47b

Co-authored-by: naturallaw777 <99053422+naturallaw777@users.noreply.github.com>

modules/core/sovran-hub.nix

@@ -99,6 +99,7 @@ let
       command_method   = "systemctl";
       role             = activeRole;
       services         = monitoredServices;
+      feature_manager  = true;
     });
 
   # ── Update wrapper script ──────────────────────────────────────
@@ -159,6 +160,39 @@ let
     exit "$RC"
   '';
 
+  # ── Rebuild wrapper script ─────────────────────────────────────
+  rebuild-script = pkgs.writeShellScript "sovran-hub-rebuild.sh" ''
+    set -uo pipefail
+    export PATH="${lib.makeBinPath [ pkgs.nix pkgs.nixos-rebuild pkgs.coreutils ]}:$PATH"
+
+    LOG="/var/log/sovran-hub-rebuild.log"
+    STATUS="/var/log/sovran-hub-rebuild.status"
+
+    echo "RUNNING" > "$STATUS"
+    : > "$LOG"
+    exec > >(tee -a "$LOG") 2>&1
+
+    echo "══════════════════════════════════════════════════"
+    echo "  Sovran_SystemsOS Rebuild — $(date)"
+    echo "══════════════════════════════════════════════════"
+    echo ""
+    echo "── Rebuilding system configuration ──────────────"
+    if nixos-rebuild switch --flake /etc/nixos --print-build-logs 2>&1; then
+      echo ""
+      echo "══════════════════════════════════════════════════"
+      echo "  ✓ Rebuild completed successfully"
+      echo "══════════════════════════════════════════════════"
+      echo "SUCCESS" > "$STATUS"
+    else
+      echo ""
+      echo "══════════════════════════════════════════════════"
+      echo "  ✗ Rebuild failed — see errors above"
+      echo "══════════════════════════════════════════════════"
+      echo "FAILED" > "$STATUS"
+      exit 1
+    fi
+  '';
+
   sovran-hub-web = pkgs.python3Packages.buildPythonApplication {
     pname   = "sovran-systemsos-hub-web";
     version = "1.0.0";
@@ -241,6 +275,32 @@ in
       };
     };
 
+    systemd.services.sovran-hub-rebuild = {
+      description = "Sovran_SystemsOS System Rebuild";
+      serviceConfig = {
+        Type      = "oneshot";
+        ExecStart = "${rebuild-script}";
+      };
+    };
+
+    systemd.services.hub-overrides-init = {
+      description = "Initialize hub-overrides.nix if missing";
+      wantedBy = [ "multi-user.target" ];
+      serviceConfig = {
+        Type            = "oneshot";
+        RemainAfterExit = true;
+      };
+      unitConfig.ConditionPathExists = "!/etc/nixos/hub-overrides.nix";
+      script = ''
+        cat > /etc/nixos/hub-overrides.nix <<'EOF'
+# Auto-generated by Sovran Hub — do not edit manually
+{ ... }:
+{
+}
+EOF
+      '';
+    };
+
     networking.firewall.allowedTCPPorts = [ 8937 ];
   };
 }