Add Nix flake for easy installation

- Package QMD as a Nix derivation with bun and sqlite dependencies
- Support `nix profile install`, `nix run`, and `nix develop`
- Set library paths for sqlite extension support

flake.nix

@@ -0,0 +1,75 @@
+{
+  description = "QMD - Quick Markdown Search";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+
+        qmd = pkgs.stdenv.mkDerivation {
+          pname = "qmd";
+          version = "1.0.0";
+
+          src = ./.;
+
+          nativeBuildInputs = [ pkgs.bun pkgs.makeWrapper ];
+
+          buildInputs = [ pkgs.sqlite ];
+
+          buildPhase = ''
+            export HOME=$(mktemp -d)
+            bun install --frozen-lockfile
+          '';
+
+          installPhase = ''
+            mkdir -p $out/lib/qmd
+            mkdir -p $out/bin
+
+            cp -r node_modules $out/lib/qmd/
+            cp qmd.ts $out/lib/qmd/
+            cp package.json $out/lib/qmd/
+
+            makeWrapper ${pkgs.bun}/bin/bun $out/bin/qmd \
+              --add-flags "$out/lib/qmd/qmd.ts" \
+              --set DYLD_LIBRARY_PATH "${pkgs.sqlite.out}/lib" \
+              --set LD_LIBRARY_PATH "${pkgs.sqlite.out}/lib"
+          '';
+
+          meta = with pkgs.lib; {
+            description = "On-device search engine for markdown notes, meeting transcripts, and knowledge bases";
+            homepage = "https://github.com/tobi/qmd";
+            license = licenses.mit;
+            platforms = platforms.unix;
+          };
+        };
+      in
+      {
+        packages = {
+          default = qmd;
+          qmd = qmd;
+        };
+
+        apps.default = {
+          type = "app";
+          program = "${qmd}/bin/qmd";
+        };
+
+        devShells.default = pkgs.mkShell {
+          buildInputs = [
+            pkgs.bun
+            pkgs.sqlite
+          ];
+
+          shellHook = ''
+            echo "QMD development shell"
+            echo "Run: bun qmd.ts <command>"
+          '';
+        };
+      }
+    );
+}