feat(prelude): hide slot render shortcut

Keep the beginner prelude on generated lower-aware render/html paths instead of exposing RenderSlotExt, which can bypass generated runtime metadata.

req: dx/006

req: component/003

req: runtime/001

REQUIREMENTS.md

@@ -76,7 +76,7 @@ slhx competes with React by making frontend frameworks unnecessary for most apps
 005	Error messages must explain fixes in author language, not internal language. Say “add `h-key="todo.id"` to this `h-for`”, not “missing ScopeKey for ResourceRef”.
 
 ### req: dx/006
-006	Generated resource methods are the preferred authoring API: `slots::todo_list.html(ui::render(&view))`, `slots::card.replace(key, view)`, `slots::count.text(42)`, `atoms::user.set(user)`. The public facade and generated view modules expose `render(view)` for trusted hemplate-to-`SafeHtml` page and fragment composition, `static_fragment(include_str!(...))` for prototype/static `.heml` fragments that need generated resource lowering as `SafeHtml`, plus `lower(html)` for callers that need the lowered string; `render_html(view)` and `lower_html(html)` remain explicit compatibility aliases. These return `impl IntoEffect`, `SafeHtml`, or lowered HTML at the boundary. Raw `Effect` constructors, opcodes, and `EffectWriter` remain low-level. [north_star]
+006	Generated resource methods are the preferred authoring API: `slots::todo_list.html(ui::render(&view))`, `slots::card.replace(key, view)`, `slots::count.text(42)`, `atoms::user.set(user)`. The public facade and generated view modules expose `render(view)` for trusted hemplate-to-`SafeHtml` page and fragment composition, `static_fragment(include_str!(...))` for prototype/static `.heml` fragments that need generated resource lowering as `SafeHtml`, plus `lower(html)` for callers that need the lowered string; `render_html(view)` and `lower_html(html)` remain explicit compatibility aliases. The beginner prelude should not expose lower-level slot render shortcuts that bypass generated lowering. These return `impl IntoEffect`, `SafeHtml`, or lowered HTML at the boundary. Raw `Effect` constructors, opcodes, and `EffectWriter` remain low-level. [north_star]
 
 ### req: dx/007
 007	Tuple composition of `IntoEffect` is the canonical batch syntax: `(a, b, c)` implements `IntoEffect` up to arity 12. `Effect::batch((...))` is available but not required for the happy path.

slhx/src/lib.rs

@@ -84,7 +84,7 @@ pub mod prelude {
         CssClasses, Effect, EventName, Form, FormModel, FormValue, Handle, IntoEffect, KeyedSlot,
         ParamName, SafeHtml, Slot,
     };
-    pub use crate::{render, render_html, RenderKeyedSlotExt, RenderSlotExt};
+    pub use crate::{render, render_html, RenderKeyedSlotExt};
     pub use slhx_derive::{app, component, form, handler, surface};
 }