Add flake.nix

.gitignore

@@ -2,3 +2,4 @@
 main
 tmp/
 build-errors.log
+result

flake.nix

@@ -0,0 +1,69 @@
+{
+  description = "Go backend template — Go HTTP server, PostgreSQL, sessions, HTMX/Alpine.js frontend";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+        go = pkgs.go_1_24;
+      in
+      {
+        packages.default = pkgs.buildGoModule {
+          pname = "go-backend";
+          version = "0.1.0";
+          src = ./.;
+
+          subPackages = [ "cmd" ];
+
+          # `go.sum` only pins 3 modules today, but this hash still has to
+          # match nix's vendor fetch. `nix build` will fail on a mismatch and
+          # print the correct value to paste in here.
+          vendorHash = "sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";
+
+          nativeBuildInputs = [ pkgs.makeWrapper ];
+
+          # The server reads templates/static assets from a relative "./ui"
+          # path (see internal/handlers/templates.go, cmd/main.go), so ship
+          # that directory next to the binary and cd there before exec,
+          # mirroring what the Dockerfile does.
+          postInstall = ''
+            mkdir -p $out/share/go-backend
+            cp -r ${./ui} $out/share/go-backend/ui
+            mv $out/bin/cmd $out/bin/go-backend
+            wrapProgram $out/bin/go-backend --run "cd $out/share/go-backend"
+          '';
+
+          meta.mainProgram = "go-backend";
+        };
+
+        apps.default = flake-utils.lib.mkApp { drv = self.packages.${system}.default; };
+
+        devShells.default = pkgs.mkShell {
+          packages = [
+            go
+            pkgs.gopls
+            pkgs.gotools
+            pkgs.delve
+            pkgs.goose
+            pkgs.sqlc
+            pkgs.air
+            pkgs.postgresql_16
+            pkgs.gnumake
+          ];
+
+          shellHook = ''
+            echo "go-backend dev shell — $(go version)"
+          '';
+        };
+
+        formatter = pkgs.nixpkgs-fmt;
+      }
+    );
+}