feat: add Nix flake for reproducible builds and deployment

- Add flake.nix with packages for all 5 apps (landing, gacha, backoffice, dimentorin, hackathon)
- Add NixOS modules for deployment (systemd service for Next.js, nginx for Vite apps)
- Add mkHackathonWithEnv function for build-time environment variables
- Add development shell with Node.js 22, npm, bun

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

nix/landing.nix

@@ -0,0 +1,50 @@
+# Next.js Landing App Package
+{ pkgs, src, npmDepsHash }:
+
+pkgs.buildNpmPackage {
+  pname = "imphnen-landing";
+  version = "0.0.1";
+  inherit src npmDepsHash;
+
+  nativeBuildInputs = with pkgs; [
+    nodejs_22
+    nodePackages.npm
+    python3  # Required for node-gyp (sharp, etc.)
+  ];
+
+  buildPhase = ''
+    runHook preBuild
+    export NX_DAEMON=false
+    export HOME=$TMPDIR
+    npm run landing:build
+    runHook postBuild
+  '';
+
+  installPhase = ''
+    runHook preInstall
+    mkdir -p $out/bin $out/share/landing
+
+    # Copy standalone server
+    cp -r dist/apps/landing/.next/standalone/* $out/share/landing/
+
+    # Copy public assets
+    mkdir -p $out/share/landing/apps/landing/public
+    cp -r dist/apps/landing/public/* $out/share/landing/apps/landing/public/ || true
+
+    # Copy static files
+    mkdir -p $out/share/landing/dist/apps/landing/.next/static
+    cp -r dist/apps/landing/.next/static/* $out/share/landing/dist/apps/landing/.next/static/
+
+    # Create wrapper script
+    cat > $out/bin/imphnen-landing <<EOF
+    #!/usr/bin/env bash
+    cd $out/share/landing
+    exec ${pkgs.nodejs_22}/bin/node apps/landing/server.js "\$@"
+    EOF
+    chmod +x $out/bin/imphnen-landing
+
+    runHook postInstall
+  '';
+
+  dontNpmBuild = true;
+}