refactor: deduplicate sha1Hex/writeJSON/writeError into pkg/utils

- admin.go: replace local sha1Hex, sha256Hex, writeJSON, writeError with pkg/utils equivalents
- auth.go: replace local writeJSON with utils.WriteJSON; rewrite writeError as thin wrapper
- cas.go: remove local sha1Hex and unused writeJSON; use utils.SHA1Bytes
- pkg/utils.go: add WriteJSON, WriteError; reorder imports

internal/auth/auth.go

@@ -17,6 +17,7 @@ import (
 
 	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/config"
 	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/database"
+	"gitea.mrixs.me/Mrixs/MrixsCraft-server/pkg/utils"
 )
 
 // Handler serves Yggdrasil endpoints.
@@ -159,7 +160,7 @@ func (h *Handler) authenticate(w http.ResponseWriter, r *http.Request) {
 		}},
 	}
 
-	writeJSON(w, http.StatusOK, resp)
+	utils.WriteJSON(w, http.StatusOK, resp)
 }
 
 func (h *Handler) refresh(w http.ResponseWriter, r *http.Request) {
@@ -216,7 +217,7 @@ func (h *Handler) refresh(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	writeJSON(w, http.StatusOK, refreshResponse{
+	utils.WriteJSON(w, http.StatusOK, refreshResponse{
 		AccessToken: newAccessToken,
 		ClientToken: req.ClientToken,
 		SelectedProfile: &profile{
@@ -356,7 +357,7 @@ func (h *Handler) sessionProfile(w http.ResponseWriter, r *http.Request) {
 		Props: props,
 	}
 
-	writeJSON(w, http.StatusOK, prof)
+	utils.WriteJSON(w, http.StatusOK, prof)
 }
 
 // ── Helpers ───────────────────────────────────────────────────
@@ -394,14 +395,8 @@ func GenerateToken() string {
 	return hex.EncodeToString(b)
 }
 
-func writeJSON(w http.ResponseWriter, status int, v any) {
-	w.Header().Set("Content-Type", "application/json")
-	w.WriteHeader(status)
-	_ = json.NewEncoder(w).Encode(v)
-}
-
 func writeError(w http.ResponseWriter, status int, err, msg string) {
-	writeJSON(w, status, errorResponse{
+	utils.WriteJSON(w, status, errorResponse{
 		Error:        err,
 		ErrorMessage: msg,
 	})