chore: add Nix flake dev shell (xcbeautify, swiftlint, swiftformat on macOS)

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 +1,57 @@
+{
+  description = "CentralCloud OnCall Mobile — ntfy iOS app (Swift/Xcode, macOS only)";
+
+  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;};
+      isDarwin = pkgs.stdenv.isDarwin;
+    in {
+      devShells.default = pkgs.mkShell {
+        packages =
+          [
+            pkgs.git
+            pkgs.jq
+          ]
+          ++ pkgs.lib.optionals isDarwin [
+            # macOS-only: Xcode toolchain is managed outside Nix via xcode-select
+            pkgs.xcbeautify   # prettier xcodebuild output
+            pkgs.swiftlint    # Swift linting
+            pkgs.swiftformat  # Swift formatting
+          ];
+
+        shellHook = ''
+          echo "CentralCloud OnCall Mobile (iOS) dev shell"
+          ${pkgs.lib.optionalString isDarwin ''
+            echo "  xcbeautify : $(xcbeautify --version 2>/dev/null || echo 'available')"
+            echo "  swiftlint  : $(swiftlint --version 2>/dev/null || echo 'available')"
+            echo ""
+            echo "Build: xcodebuild -scheme ntfy -destination 'generic/platform=iOS' | xcbeautify"
+            echo "Note : Xcode must be installed via xcode-select (not managed by Nix)"
+          ''}
+          ${pkgs.lib.optionalString (!isDarwin) ''
+            echo ""
+            echo "NOTE: iOS builds require macOS + Xcode. This shell provides only"
+            echo "      scripting utilities on Linux/other platforms."
+          ''}
+        '';
+      };
+    });
+}