Guide the model to present pages for page-like deliverables

Why: Field evidence from the dev instance - the present tool was
projected and enabled but never called, because every resident prompt
module steers 'make me a report' toward file artifacts; the tool
description carried only the component catalog, not when to use it.

Evidence: genui suite green (catalog assertion extended implicitly by
existing shape test); end-to-end model behavior verified post-deploy
in the Dev task.

Impact: Tool description text only (self-gating: description appears
only when the activation gate projects the tool).

Refs: Dev task fix/genui-page-visibility
EOF
)

internal/genui/genui.go

@@ -27,7 +27,9 @@ const (
 
 // Catalog 是组件目录与纪律（U1 试验 CATALOG_PROMPT 的 Go 权威版；工具描述携带，
 // 模型与校验器看到同一份规则）。修改需同步 core.ValidateSurfaceSpec 与目录版本。
-const Catalog = `可用节点类型（16 种；字段必须严格匹配，禁止目录外类型/字段）：
+const Catalog = `何时用本工具：用户要求"整理成一页 / 做个对比 / 出一页报告 / 看板 / 时间线"这类**页面化交付**时，优先调用本工具提交声明式页面，而不是写文件工件——页面会在用户预览区直接打开并可继续修订。纯文本问答、简短列表、代码交付保持原方式，不强行出页。
+
+可用节点类型（16 种；字段必须严格匹配，禁止目录外类型/字段）：
 section{title?,children?}；list{items:string[]}；kv{kv:[[k,v]]}；
 form{fields:[{key,label,type:text|textarea|number|boolean|select,options?(select必填),required?,placeholder?,help?,default?}]}；
 markdown{markdown}；doc-ref{docId}(须为会话内存在的工件ID)；