docs(ui): react-pages html-tier names are verbatim, not kebab-case

The html-tier spelling paragraph in react-pages.mdx told authors that
registered block names are "lowercase and kebab-case", but four
registered names (record:line_items, record:quick_actions,
record:reference_rail, record:related_list) are snake_case after
their namespace prefix. The sdui-parser whitelist is an exact
Set.has comparison with no case folding or separator normalisation,
so a kebab-case respelling of one of those names (record:related-list)
is rejected at save time exactly like a PascalCase borrow.

Drop the "lowercase and kebab-case" gloss, let the verbatim rule
stand on its own, and add a second snake_case example
(record:line_items) plus a concrete negative example so the shape is
demonstrated rather than described.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Vbw3RPgdtqesx4azk9SbW8

Author: claude

content/docs/ui/react-pages.mdx

@@ -31,9 +31,12 @@ tags in the public block manifest are accepted, props are checked against each b
 declared inputs, and an unknown tag is a hard error at save time. That is the tier for
 author- or AI-generated pages you have not reviewed.
 
-Those tags are the **registered type names, written verbatim** — lowercase and
-kebab-case, keeping the namespace prefix where a block has one: `<list-view>`,
-`<object-form>`, `<object-chart>`, `<record:related_list>`, `<flex>`. The **PascalCase**
+Those tags are the **registered type names, written verbatim** — whatever the registry
+spells, character for character, including a `record:` / `page:` / `element:` /
+`action:` namespace prefix and any underscore inside the name: `<list-view>`,
+`<object-form>`, `<object-chart>`, `<record:related_list>`, `<record:line_items>`,
+`<flex>`. A name re-spelled to look uniform is not registered: `<record:related-list>`
+is rejected at save time, only `<record:related_list>` exists. The **PascalCase**
 spellings further down this page (`<ListView>`, `<ObjectForm>`, `<ObjectChart>`) are the
 **react tier's** convention and are not registered names, so an html page that borrows
 one is rejected at save time with `<ListView> is not an allowed component`.