feat(nbd): add Nix flake for building and running nbd [6e4239]

Add flake.nix so nbd can be consumed as a reproducible Nix package.
Exposes packages.default, apps.default (nix run), and a devShell with
stable Rust toolchain and the nbd binary. Uses cargoLock for
dependency hashing without a pre-computed cargoHash.

Also adds an Installation section to README.md covering nix run and
nix build usage.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nbd/.nbd/tickets/6e4239.md

@@ -1,7 +1,7 @@
 +++
 title = "Nix flake for nbd"
 priority = 4
-status = "todo"
+status = "done"
 ticket_type = "task"
 dependencies = []
 +++

nbd/README.md

@@ -177,6 +177,38 @@ nbd migrate --dry-run   # preview changes without writing
 nbd migrate --json      # machine-readable summary
 ```
 
+## Installation
+
+### Nix (recommended)
+
+Run directly without installing, using the bundled Nix flake:
+
+```sh
+nix run github:elijah/vibed?dir=nbd -- --help
+```
+
+Or add to a Nix devShell:
+
+```nix
+{
+  inputs.nbd.url = "github:elijah/vibed?dir=nbd";
+  # then use nbd.packages.${system}.nbd in your devShell packages
+}
+```
+
+Build locally from the `nbd/` directory:
+
+```sh
+nix build        # builds the nbd binary
+nix run -- init  # run nbd init via nix run
+```
+
+### Cargo
+
+```sh
+cargo install --path .
+```
+
 ## Running
 
 ```sh

nbd/flake.nix

@@ -0,0 +1,98 @@
+{
+  description = "nbd — CLI tool for managing work tickets, targeted at agent workflows";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    rust-overlay = {
+      url = "github:oxalica/rust-overlay";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs =
+    {
+      self,
+      nixpkgs,
+      rust-overlay,
+    }:
+    let
+      systems = [
+        "x86_64-linux"
+        "aarch64-linux"
+        "x86_64-darwin"
+        "aarch64-darwin"
+      ];
+
+      forAllSystems =
+        f:
+        nixpkgs.lib.genAttrs systems (
+          system:
+          f {
+            inherit system;
+            pkgs = import nixpkgs {
+              inherit system;
+              overlays = [ rust-overlay.overlays.default ];
+            };
+          }
+        );
+    in
+    {
+      packages = forAllSystems (
+        { pkgs, system }:
+        {
+          # The nbd CLI package, built with rustPlatform.buildRustPackage.
+          nbd = pkgs.rustPlatform.buildRustPackage {
+            pname = "nbd";
+            version = "0.1.0";
+
+            src = ./.;
+
+            cargoLock = {
+              lockFile = ./Cargo.lock;
+            };
+
+            meta = {
+              description = "CLI tool for managing work tickets, targeted at agent workflows";
+              license = with pkgs.lib.licenses; [
+                asl20
+                mit
+              ];
+              mainProgram = "nbd";
+            };
+          };
+
+          # Make nbd the default package so `nix build` works without specifying an attribute.
+          default = self.packages.${system}.nbd;
+        }
+      );
+
+      apps = forAllSystems (
+        { system, ... }:
+        {
+          # Run nbd directly with `nix run .#nbd`.
+          nbd = {
+            type = "app";
+            program = "${self.packages.${system}.nbd}/bin/nbd";
+          };
+
+          # Make nbd the default app so `nix run` works without specifying an attribute.
+          default = self.apps.${system}.nbd;
+        }
+      );
+
+      devShells = forAllSystems (
+        { pkgs, system }:
+        {
+          # Development shell with stable Rust toolchain and nbd binary.
+          default = pkgs.mkShell {
+            packages = [
+              # Stable Rust toolchain: compiler, cargo, rustfmt, clippy.
+              pkgs.rust-bin.stable.latest.default
+              # The built nbd binary, available as `nbd` in the shell.
+              self.packages.${system}.nbd
+            ];
+          };
+        }
+      );
+    };
+}