docs(requirements): split handler rows

Add explicit ring fields to derive_handler requirements and split handler parameter constraints without changing behavior.

req: derive_handler/001

req: derive_handler/002

req: derive_handler/003

req: derive_handler/004

req: derive_handler/005

README.md

@@ -35,8 +35,8 @@ For beginner and production-shaped app code, stay on this path. req: public_api/
    hemplate Surface and emits generated Rust helpers for slots, forms, handles,
    page targets, classes, and events. req: ceremony/003 req: build/001
 3. **Handlers are plain Rust.** App code uses `#[hemx::handler]` functions with
-   ordinary domain types, framework extractors, generated `Form<T>` inputs, and
-   `impl IntoEffect` or `Result<impl IntoEffect, E>` returns. req: derive_handler/004
+   ordinary domain types, framework extractors, generated `Form<T>` inputs,
+   explicit `data-*` params, and `impl IntoEffect` or fallible returns. req: derive_handler/001 req: derive_handler/002 req: derive_handler/003 req: derive_handler/004 req: derive_handler/005
 4. **Handlers return generated commands.** Common handlers return helpers such
    as `todos.append(todo)`, `todo_row.replace(row)`, `new_todo.error("title",
    "Required")`, `new_todo.clear()`, `page.replace(view)`, or tuples of those