feat: nix flake with package, NixOS module and dev shell

nix run / nix build produce a wrapped CLI that pins libpcsclite by store
path, the package build runs the test suite (so nix flake check is CI),
programs.boltcard-writer.enable installs it and turns on pcscd, and
nix develop / nix-shell give the uv workflow used on Arch.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1789785513,
+        "narHash": "sha256-B44WL6h0XoLjJ41bUPJk0X5SDinLCII//6EcBLXKiJ0=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "20b1ddd1aa5ace70c9468305030aa4f9ef79671b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}