feat: admin skill public upload + user management page

- Admin users can choose to install skills to public (built-in) or custom category via UI radio selector in InstallSkillDialog
- Backend: SkillStorage.ainstall_skill_from_archive accepts target_category param; non-admin 403 on public install
- Backend: AgentStore/SkillStore add count_owned(user_id); UserRepository/LocalAuthProvider add list_users()
- Backend: GET /api/v1/auth/users endpoint (admin-only) returns all users with skill_count and agent_count
- Frontend: admin-only "用户管理" nav item in sidebar; /page/workspace/admin/users route with user table
- i18n: added sidebar.users and adminUsers section in zh-CN/en-US

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend-web/src/components/workspace/settings/skill-settings-page.tsx

@@ -160,6 +160,7 @@ function SkillSettingsList({
       <InstallSkillDialog
         open={installOpen}
         onClose={() => setInstallOpen(false)}
+        isAdmin={isAdmin}
       />
     </div>
   );
@@ -358,9 +359,11 @@ function EmptySkill({ onCreateSkill }: { onCreateSkill: () => void }) {
 function InstallSkillDialog({
   open,
   onClose,
+  isAdmin,
 }: {
   open: boolean;
   onClose: () => void;
+  isAdmin: boolean;
 }) {
   const { t } = useI18n();
   const dialog = t.settings.skills.installDialog;
@@ -369,6 +372,7 @@ function InstallSkillDialog({
   const [validation, setValidation] = useState<ValidateSkillUploadResponse | null>(null);
   const [validationError, setValidationError] = useState<string | null>(null);
   const [isDragging, setIsDragging] = useState(false);
+  const [targetCategory, setTargetCategory] = useState<"custom" | "public">("custom");
   const validateMutation = useValidateSkillUpload();
   const installMutation = useInstallSkillUpload();
 
@@ -377,6 +381,7 @@ function InstallSkillDialog({
     setValidation(null);
     setValidationError(null);
     setIsDragging(false);
+    setTargetCategory("custom");
     if (inputRef.current) inputRef.current.value = "";
   }, []);
 
@@ -433,7 +438,7 @@ function InstallSkillDialog({
     async (overwrite: boolean) => {
       if (!file) return;
       try {
-        const result = await installMutation.mutateAsync({ file, overwrite });
+        const result = await installMutation.mutateAsync({ file, overwrite, targetCategory });
         toast.success(
           (result.overwritten ? dialog.installSuccessReplaced : dialog.installSuccess).replace(
             "{name}",
@@ -446,13 +451,15 @@ function InstallSkillDialog({
         toast.error(err instanceof Error ? err.message : String(err));
       }
     },
-    [dialog.installSuccess, dialog.installSuccessReplaced, file, installMutation, onClose, reset],
+    [dialog.installSuccess, dialog.installSuccessReplaced, file, installMutation, onClose, reset, targetCategory],
   );
 
   const isPublicConflict = validation?.conflict && validation.conflict_kind === "public";
   const isCustomConflict = validation?.conflict && validation.conflict_kind === "custom";
-  const canInstall = !!validation && !validationError && !isPublicConflict && !isCustomConflict;
-  const canOverwrite = !!validation && !validationError && isCustomConflict;
+  // Admin targeting public directory can overwrite an existing public skill.
+  const adminCanOverwritePublic = isAdmin && targetCategory === "public" && !!isPublicConflict;
+  const canInstall = !!validation && !validationError && !isCustomConflict && (adminCanOverwritePublic ? false : !isPublicConflict);
+  const canOverwrite = !!validation && !validationError && (!!isCustomConflict || adminCanOverwritePublic);
 
   return (
     <Dialog open={open} onOpenChange={(o) => !o && handleClose()}>
@@ -500,6 +507,27 @@ function InstallSkillDialog({
             />
           </div>
 
+          {isAdmin && (
+            <div className="flex items-center gap-3 text-sm">
+              <span className="text-muted-foreground shrink-0">{dialog.targetCategoryLabel}</span>
+              <div className="flex gap-4">
+                {(["custom", "public"] as const).map((cat) => (
+                  <label key={cat} className="flex cursor-pointer items-center gap-1.5">
+                    <input
+                      type="radio"
+                      name="targetCategory"
+                      value={cat}
+                      checked={targetCategory === cat}
+                      onChange={() => setTargetCategory(cat)}
+                      className="accent-primary"
+                    />
+                    <span>{cat === "custom" ? dialog.categoryCustom : dialog.categoryPublic}</span>
+                  </label>
+                ))}
+              </div>
+            </div>
+          )}
+
           {validateMutation.isPending && (
             <div className="text-muted-foreground flex items-center gap-2 text-sm">
               <Loader2 className="size-4 animate-spin" />
@@ -557,10 +585,10 @@ function InstallSkillDialog({
                 </div>
               )}
               {isPublicConflict && (
-                <div className="text-destructive mt-1 flex items-start gap-2 text-xs">
+                <div className={cn("mt-1 flex items-start gap-2 text-xs", adminCanOverwritePublic ? "text-amber-600" : "text-destructive")}>
                   <AlertCircle className="mt-0.5 size-3.5 shrink-0" />
                   <span>
-                    {dialog.conflictPublic.replace("{name}", validation.skill_name)}
+                    {(adminCanOverwritePublic ? dialog.conflictPublicAdminHint : dialog.conflictPublic).replace("{name}", validation.skill_name)}
                   </span>
                 </div>
               )}