chore: add Nix flake dev shell + package (Go 1.24, Node 20, golangci-lint, goreleaser)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

flake.lock

@@ -0,0 +1,61 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1778003029,
+        "narHash": "sha256-q/nkKLDtHIyLjZpKhWk3cSK5IYsFqtMd6UtXF3ddjgA=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "0c88e1f2bdb93d5999019e99cb0e61e1fe2af4c5",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-25.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,71 @@
+{
+  description = "CentralCloud ntfy server fork — push notification backend for oncall alerts";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.11";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  nixConfig = {
+    extra-substituters = [
+      "https://cache.centralcloud.com/default"
+    ];
+    extra-trusted-public-keys = [
+      "default:ywfU21WX06iOn2Ec2lae1jYh4w8LO4IQkmp06vJzsk8="
+    ];
+  };
+
+  outputs = {
+    nixpkgs,
+    flake-utils,
+    ...
+  }:
+    flake-utils.lib.eachDefaultSystem (system: let
+      pkgs = import nixpkgs {inherit system;};
+    in {
+      devShells.default = pkgs.mkShell {
+        packages = with pkgs; [
+          go_1_24
+          gotools        # goimports, godoc, etc.
+          golangci-lint
+          goreleaser
+
+          # Frontend (web UI)
+          nodejs_20
+          nodePackages.npm
+
+          # Dev tooling
+          gnumake
+          git
+          curl
+          jq
+        ];
+
+        shellHook = ''
+          export GOPATH="$HOME/go"
+          export PATH="$GOPATH/bin:$PATH"
+          echo "CentralCloud ntfy server dev shell"
+          echo "  go      : $(go version)"
+          echo "  node    : $(node --version)"
+          echo ""
+          echo "Run:   go run main.go serve"
+          echo "Build: make build"
+          echo "Test:  go test ./..."
+        '';
+      };
+
+      packages.default = pkgs.buildGoModule {
+        pname = "ntfy";
+        version = "2.22.0";
+        src = ./.;
+        vendorHash = null;
+        doCheck = false;
+        meta = {
+          description = "Send push notifications to your phone or desktop via PUT/POST";
+          homepage = "https://ntfy.sh";
+          license = pkgs.lib.licenses.asl20;
+          mainProgram = "ntfy";
+        };
+      };
+    });
+}