cmd/genjwks: print to stdout instead of writing to file

also setup nix devshell to configure TANGLED_OAUTH_JWK in a shellhook
for seamless local oauth dev.

cmd/genjwks/main.go

···
 	"crypto/rand"
 	"encoding/json"
 	"fmt"
-	"os"
 	"time"
 
 	"github.com/lestrrat-go/jwx/v2/jwk"
···
 		panic(err)
 	}
 
-	if err := os.WriteFile("./jwks.json", b, 0644); err != nil {
-		panic(err)
-	}
+	fmt.Println(string(b))
 }

flake.nix

···
       };
       repoguard = buildCmdPackage "repoguard";
       keyfetch = buildCmdPackage "keyfetch";
+      genjwks = buildCmdPackage "genjwks";
     };
     packages = forAllSystems (system: {
       inherit
···
         knotserver-unwrapped
         repoguard
         keyfetch
+        genjwks
         ;
     });
     defaultPackage = forAllSystems (system: nixpkgsFor.${system}.appview);
···
           cp -f ${inter-fonts-src}/web/InterVariable*.woff2 appview/pages/static/fonts/
           cp -f ${inter-fonts-src}/web/InterDisplay*.woff2 appview/pages/static/fonts/
           cp -f ${ibm-plex-mono-src}/fonts/complete/woff2/IBMPlexMono-Regular.woff2 appview/pages/static/fonts/
+          export TANGLED_OAUTH_JWKS="$(${pkgs.genjwks}/bin/genjwks)"
         '';
         env.CGO_ENABLED = 1;
       };