feat(admin): hide the batch-create entry unless snapshot sharing is on

- a batch clones every user from a shared snapshot code, and handleUserBatch
  already refuses when snapshots.share is off; the entry point now follows, so
  the admin is not offered a form that can only be rejected
- carry snapshot-sharing state into the admin page data (ShareEnabled)
- correct the snapshots.share help text, which still claimed "default true"
  although sharing is an explicit opt-in and defaults to false

src/internal/admin/admin_test.go

@@ -1278,12 +1278,13 @@ func TestUserBatchStatus(t *testing.T) {
 }
 
 // TestOverviewBatchUI checks the batch entry point and form render, including
-// the admin-key checkboxes and the empty-store hint.
+// the admin-key checkboxes and the empty-store hint, and that the entry point
+// is hidden while snapshot sharing is off (a batch clones from a share code).
 func TestOverviewBatchUI(t *testing.T) {
 	srv, _ := newTestServer(t)
 
 	withKeys := srv.renderToString(t, "admin_overview.html", pageData{
-		Prefix: "/" + testAdminSecret, Lang: langEn,
+		Prefix: "/" + testAdminSecret, Lang: langEn, ShareEnabled: true,
 		AdminKeys: []sshKeyRow{{ID: 5, Name: "ops-host", Key: "ssh-ed25519 AAAABODY ops-host", Active: true}},
 	})
 	for _, want := range []string{
@@ -1294,6 +1295,11 @@ func TestOverviewBatchUI(t *testing.T) {
 			t.Errorf("batch UI missing %q", want)
 		}
 	}
+	// Snapshot sharing off (the default): no invitation to start a batch.
+	hidden := srv.renderToString(t, "admin_overview.html", pageData{Prefix: "/" + testAdminSecret, Lang: langEn})
+	if strings.Contains(hidden, `id="batchBtn"`) {
+		t.Error("batch entry point must be hidden while snapshot sharing is off")
+	}
 	// "No keys yet" also appears (hidden) in the pre-existing SSH-keys modal,
 	// so assert on this form's own wording.
 	const emptyHint = "No admin keys"

src/internal/admin/handlers.go

@@ -64,6 +64,10 @@ type pageData struct {
 	// BatchID, when set, is a running/recent batch create the page should show
 	// the progress modal for (carried through the redirect after submitting).
 	BatchID string
+	// ShareEnabled gates the batch-create entry point: a batch clones every user
+	// from a shared snapshot code, so with snapshot sharing off there is nothing
+	// to create from (the handler refuses the same way).
+	ShareEnabled bool
 	// Global dynamic CPU limit rule, edited by the card below (the DB is the
 	// single source of truth — there is no config.yaml / CLI equivalent). The
 	// Active list is the containers currently capped by it.
@@ -150,13 +154,14 @@ type userView struct {
 func (s *Server) buildPageData(msg, errMsg string) pageData {
 	v4Caps := s.mgr.LiveV4Capabilities()
 	d := pageData{
-		Title:    "VPS Manager Admin",
-		Prefix:   s.prefix(),
-		Msg:      msg,
-		Err:      errMsg,
-		V4Policy: s.mgr.LiveV4Policy(),
-		DirectV4: v4Caps.DirectForwarding,
-		Colors:   append([]string{}, userColorPalette...),
+		Title:        "VPS Manager Admin",
+		Prefix:       s.prefix(),
+		Msg:          msg,
+		Err:          errMsg,
+		V4Policy:     s.mgr.LiveV4Policy(),
+		DirectV4:     v4Caps.DirectForwarding,
+		ShareEnabled: s.mgr.SnapshotShareEnabled(),
+		Colors:       append([]string{}, userColorPalette...),
 	}
 	hs := s.mgr.HostStats()
 	d.Reboot = hs.RebootNeeded

src/internal/admin/templates/admin_overview.html

@@ -223,7 +223,7 @@ a.copy.copied { border-color: #86efac; background: #dcfce7; color: #15803d; }
 
   <div class="card">
     <h2>{{if eq .Lang "zh"}}创建用户{{else}}Create user{{end}}</h2>
-    <div style="margin:-4px 0 10px"><button type="button" class="btn" id="batchBtn">{{if eq .Lang "zh"}}批量创建用户{{else}}Batch create{{end}}</button></div>
+    {{if .ShareEnabled}}<div style="margin:-4px 0 10px"><button type="button" class="btn" id="batchBtn">{{if eq .Lang "zh"}}批量创建用户{{else}}Batch create{{end}}</button></div>{{end}}
     <div class="plans" id="plans"></div>
     <form action="{{.Prefix}}/user-add" method="post" class="form-grid" id="createForm">
       <div class="field create-field name-field"><label>{{if eq .Lang "zh"}}用户名{{else}}Username{{end}}</label><input name="name" id="cfName" pattern="[a-z]([a-z0-9-]*[a-z0-9])?" maxlength="31" autocomplete="off" required title="{{if eq .Lang "zh"}}小写字母开头和结尾，仅含小写字母、数字和连字符{{else}}start/end with a lowercase letter; lowercase letters, digits, hyphens only{{end}}"><small id="cfNameHint" style="color:#6b7280;display:block;margin-top:4px;min-height:1em">{{if eq .Lang "zh"}}自动转为小写{{else}}Folded to lowercase{{end}}</small></div>

src/internal/cfg/registry.go

@@ -449,7 +449,7 @@ var Fields = []Field{
 			return nil
 		}},
 	{"snapshots.share", KindOperator, ApplyImmediate,
-		"allow users to share a checkpoint behind a code and install a container from it (default true); stored codes are kept when turned off",
+		"allow users to share a checkpoint behind a code and install a container from it (off by default; explicit opt-in); stored codes are kept when turned off",
 		"true or false",
 		getStr(func(c *Config) string { return strconv.FormatBool(c.Snapshots.Share) }),
 		func(c *Config, v string) error {