Add a flake.nix for Nix packaging; document nix install paths in README

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -11,6 +11,20 @@ cargo build --release
 # target/release/calcalist
 ```
 
+With Nix flakes enabled:
+
+```sh
+nix build   # ./result/bin/calcalist
+# or: nix run . -- doctor
+# or: nix profile install .
+```
+
+Or straight from the repo, without cloning it first:
+
+```sh
+nix profile install "git+https://code.randogoth.com/randogoth/CalCalist.git"
+```
+
 One runtime dependency is needed for CalDAV and iCal sync: **`pimsync` 0.5.x on `PATH`**.
 
 Then check the environment, which is worth doing before writing any config:

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1789006805,
+        "narHash": "sha256-xB8mKMOx1IA9vTDNLmJZ6n4wCMq/cuWBBOzGCRnqxrU=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "8ce4ef6cb6f871616146b9fe26d2a5ae594e94fe",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,53 @@
+{
+  description = "Aggregate and sync events between CalDAV, Google Calendar and iCal feeds";
+
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  outputs =
+    { self, nixpkgs }:
+    let
+      systems = [
+        "x86_64-linux"
+        "aarch64-linux"
+      ];
+      forEachSystem = nixpkgs.lib.genAttrs systems;
+      cargoToml = builtins.fromTOML (builtins.readFile ./Cargo.toml);
+    in
+    {
+      packages = forEachSystem (
+        system:
+        let
+          pkgs = import nixpkgs { inherit system; };
+        in
+        rec {
+          calcalist = pkgs.rustPlatform.buildRustPackage {
+            pname = "calcalist";
+            version = cargoToml.package.version;
+            src = pkgs.lib.cleanSource ./.;
+            cargoLock.lockFile = ./Cargo.lock;
+
+            # tests/caldav.rs spins up radicale and pimsync as real
+            # processes; it's a dev-time integration gate (devbox run
+            # check), not something a package build should re-run.
+            doCheck = false;
+
+            meta = {
+              description = cargoToml.package.description;
+              license = pkgs.lib.licenses.mit;
+              mainProgram = "calcalist";
+              platforms = pkgs.lib.platforms.linux;
+            };
+          };
+          default = calcalist;
+        }
+      );
+
+      apps = forEachSystem (system: rec {
+        calcalist = {
+          type = "app";
+          program = "${self.packages.${system}.calcalist}/bin/calcalist";
+        };
+        default = calcalist;
+      });
+    };
+}