Add vendored RTL package and fix rtl.nix to use it

- Create packages/rtl/default.nix to build RTL from source
- Update modules/bitcoin/rtl.nix to use vendored package instead of pkgs.rtl
- Remove clightning/lightning-loop references (Sovran is LND-only)
- Simplify to LND-only configuration

packages/rtl/default.nix

@@ -0,0 +1,65 @@
+{ lib
+, stdenvNoCC
+, nodejs_22
+, nodejs-slim_22
+, fetchurl
+, makeWrapper
+}:
+
+let
+  version = "0.15.8";
+
+  src = fetchurl {
+    url = "https://github.com/Ride-The-Lightning/RTL/archive/refs/tags/v${version}.tar.gz";
+    hash = "sha256-8XdGyORxB2dkZRB/Yl7zh+Quqo4L/Y0VmC6Brbr/hqU=";
+  };
+
+in stdenvNoCC.mkDerivation {
+  pname = "rtl";
+  inherit version src;
+
+  nativeBuildInputs = [
+    makeWrapper
+    nodejs_22
+  ];
+
+  phases = "unpackPhase buildPhase installPhase";
+
+  buildPhase = ''
+    # Install dependencies using npm ci (requires package-lock.json)
+    npm ci --legacy-peer-deps --ignore-scripts
+  '';
+
+  # `src` already contains the precompiled frontend and backend.
+  # Copy all files required for packaging, like in
+  # https://github.com/Ride-The-Lightning/RTL/blob/master/dockerfiles/Dockerfile
+  installPhase = ''
+    dest=$out/lib/node_modules/rtl
+    mkdir -p $dest
+    cp -r \
+      rtl.js \
+      package.json \
+      frontend \
+      backend \
+      node_modules \
+      $dest
+
+    makeWrapper ${nodejs-slim_22}/bin/node "$out/bin/rtl" \
+      --add-flags "$dest/rtl.js"
+
+    runHook postInstall
+  '';
+
+  passthru = {
+    nodejs = nodejs_22;
+    nodejsRuntime = nodejs-slim_22;
+  };
+
+  meta = with lib; {
+    description = "A web interface for LND";
+    homepage = "https://github.com/Ride-The-Lightning/RTL";
+    license = licenses.mit;
+    maintainers = with maintainers; [ ];
+    platforms = platforms.unix;
+  };
+}