fix(nix): use proper bash path in wrapper script

Fix wrapper script to use explicit Nix bash path instead of
/usr/bin/env bash which doesn't work on NixOS.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

nix/landing.nix

@@ -46,7 +46,7 @@ pkgs.buildNpmPackage {
 
     # Create wrapper script
     cat > $out/bin/imphnen-landing <<EOF
-    #!/usr/bin/env bash
+    #!${pkgs.bash}/bin/bash
     cd $out/share/landing
     exec ${pkgs.nodejs_22}/bin/node apps/landing/server.js "\$@"
     EOF