feat(flake): add .deb packaging with shell completions

Add mkStreamdDeb function that uses nfpm to create a .deb package
containing the statically-linked binary and shell completions for
bash, zsh, and fish.

flake.nix

@@ -131,6 +131,48 @@
           cargoArtifacts = craneLib.buildDepsOnly commonArgs;
         in
         craneLib.buildPackage (commonArgs // { inherit cargoArtifacts; });
+
+      mkStreamdDeb =
+        system:
+        let
+          pkgs = mkPkgs system;
+          streamd-musl = mkStreamdMusl system;
+        in
+        pkgs.runCommand "streamd_${version}_amd64.deb" {
+          nativeBuildInputs = [ pkgs.nfpm ];
+        } ''
+          # Generate shell completions
+          mkdir -p completions
+          ${streamd-musl}/bin/streamd completions bash > completions/streamd.bash
+          ${streamd-musl}/bin/streamd completions zsh > completions/_streamd
+          ${streamd-musl}/bin/streamd completions fish > completions/streamd.fish
+
+          cat > nfpm.yaml <<EOF
+          name: streamd
+          arch: amd64
+          platform: linux
+          version: "${version}"
+          maintainer: Konstantin Fickel
+          description: Personal knowledge management and time-tracking CLI using @Tag annotations
+          license: AGPL-3.0-only
+          homepage: https://git.konstantinfickel.de/kfickel/streamd
+          contents:
+            - src: ${streamd-musl}/bin/streamd
+              dst: /usr/bin/streamd
+              file_info:
+                mode: 0755
+            - src: completions/streamd.bash
+              dst: /usr/share/bash-completion/completions/streamd
+            - src: completions/_streamd
+              dst: /usr/share/zsh/vendor-completions/_streamd
+            - src: completions/streamd.fish
+              dst: /usr/share/fish/vendor_completions.d/streamd.fish
+          deb:
+            compression: gzip
+          EOF
+
+          nfpm package --config nfpm.yaml --packager deb --target $out
+        '';
     in
     {
       packages = forAllSystems (