flake: drop flake-utils, match hyperhive's hand-rolled forAllSystems

mara on PR #1: \"never use flake utils - look at hyperhive flake\".

Rewrote the flake to mirror hyperhive's pattern:

- Single `nixpkgs` input (no `flake-utils`, no `treefmt-nix`,
  no `naersk` — none apply to a static-site dist).
- Hand-rolled `forAllSystems` over `[aarch64-linux, x86_64-linux]`
  via `lib.genAttrs`. Same shape as `hyperhive/hyperhive`'s flake
  so contributors see consistent ceremony across both repos.
- `packages.<system>.website` builds the dist; `packages.<system>.default`
  points at it. `devShells.<system>.default` exposes `zola` for the
  `zola serve` dev loop.
- Dropped the `apps.default` shortcut — `zola serve` is more usefully
  spelled `nix develop -c zola serve` since dev needs the whole shell
  anyway.

Also dropped the auto-generated flake.lock that the old
flake-utils tree had written; nix will regenerate it on first
`nix build` against the new inputs.

flake.lock

@@ -1,61 +0,0 @@
-{
-  "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": 1779560665,
-        "narHash": "sha256-tpyBcxPpcQb8ukyNF7DoCwfSY3VPsxHoYwj00Cayv5o=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "64c08a7ca051951c8eae34e3e3cb1e202fe36786",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "ref": "nixos-unstable",
-        "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

@@ -4,19 +4,39 @@
   # `nix build` → `result/` is the `public/` Zola dist, ready to drop
   # under any static-file host. No CI runner needed; the flake is the
   # validation contract.
+  #
+  # Output shape mirrors `hyperhive/hyperhive`'s flake — hand-rolled
+  # `forAllSystems` helper instead of `flake-utils`. Less ceremony,
+  # one source of truth for the systems list, and consistent with the
+  # rest of the project.
   description = "hyperhive marketing landing";
 
-  inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
-    flake-utils.url = "github:numtide/flake-utils";
-  };
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.11";
 
-  outputs = { self, nixpkgs, flake-utils }:
-    flake-utils.lib.eachDefaultSystem (system:
+  outputs =
+    { self, nixpkgs }:
     let
-        pkgs = import nixpkgs { inherit system; };
-      in {
-        packages.website = pkgs.stdenv.mkDerivation {
+      inherit (nixpkgs) lib;
+      systems = [
+        "aarch64-linux"
+        "x86_64-linux"
+      ];
+      forAllSystems =
+        f:
+        lib.genAttrs systems (
+          system:
+          f rec {
+            inherit system;
+            pkgs = nixpkgs.legacyPackages.${system};
+          }
+        );
+    in
+    {
+      packages = forAllSystems (
+        { pkgs, ... }:
+        {
+          # `nix build .#website` → static dist at result/.
+          website = pkgs.stdenv.mkDerivation {
             pname = "hyperhive-website";
             version = self.shortRev or "dev";
 
@@ -24,10 +44,9 @@
 
             nativeBuildInputs = [ pkgs.zola ];
 
-          # Zola reads `config.toml` from CWD, writes `public/` next to it,
-          # which we then move to $out. The build is offline / hermetic —
-          # no network access needed at build time, which fits the nix
-          # sandbox without extra fetchurls.
+            # Zola reads `config.toml` from CWD, writes `public/` next to
+            # it. Build is offline / hermetic — no network access needed
+            # at build time, fits the nix sandbox without extra fetchurls.
             buildPhase = ''
               runHook preBuild
               zola build --output-dir public
@@ -46,19 +65,19 @@
           };
 
           # `nix build` with no attribute → the website dist.
-        packages.default = self.packages.${system}.website;
+          default = self.packages.${pkgs.system}.website;
+        }
+      );
 
       # `nix develop` → a shell with zola for local iteration:
       #   `zola serve` runs the dev server with live reload.
-        devShells.default = pkgs.mkShell {
+      devShells = forAllSystems (
+        { pkgs, ... }:
+        {
+          default = pkgs.mkShell {
             packages = [ pkgs.zola ];
           };
-
-        # `nix run` is the dev-server shortcut: `nix run . -- serve`
-        # boots Zola's hot-reload server on http://127.0.0.1:1111/.
-        apps.default = {
-          type = "app";
-          program = "${pkgs.zola}/bin/zola";
-        };
-      });
+        }
+      );
+    };
 }