improvement(docs): clean up leftovers from the code-block alignment PR (#6825)

* improvement(docs): clear leftovers from the reverted revisions

A cleanup pass over the final state. Every finding was residue from an approach
this PR tried and abandoned, or a claim that stopped being true when it did.

- Delete the copy-button svg sizing rule: a later rule sets `display: none` on
  that same element ungated, so sizing it was never observable. Superseded by
  the mask approach.
- Drop the paragraph in page.tsx arguing about a custom Shiki factory. The
  factory was deleted; nothing configures one now.
- Correct shiki-curl-json.ts, which still claimed the grammar "reaches the
  client path too". It does not — that was the justification for choosing a
  grammar over a transformer, so leaving it stated the opposite of the truth.
  Now records where it applies, where it does not, and why not to retry.
- Correct the global.css section header, which claimed the component owns the
  shell while the next rule defines it here.
- Qualify the `--copy-glyph` declarations with `:has(> svg[class*="lucide"])`,
  which the group's own comment asserts of every rule in it.
- Correct `getCode`'s TSDoc: the gutter is a `::before`, and pseudo-element
  content never reaches `textContent`, so line numbers were never what the
  clone guards. It guards transformer-emitted `.nd-copy-ignore` nodes.
- Compose `chipGeometryClass` and emcn's `ChipChevronDown` in the API example
  selector instead of restating their literals.
- Merge the duplicated `div[role="region"]` rule. The tablist pair stays split:
  biome's `noDuplicateProperties` reads a nested `@variant` setting the same
  property as a duplicate and fails the build — recorded so it is not remerged.
- Note that fumadocs ships its own gutter for `lines`-meta fences, which cannot
  be suppressed from here and would paint a second column.

* fix(docs): drop a highlighter registration that can never fire

fumadocs-openapi calls `renderCodeBlock` with a hard-coded `"json"` from both of
its call sites (`request-tabs.js:76`, `response-tabs.js:48`), so the docs
`CodeBlock` it routes through never receives a shell language. The
`getHighlighter('js', { langs: [curlJsonBodyGrammar] })` registering the
shell-scoped JSON-body injection therefore did nothing but await on every API
sample render, and the docblock claiming the grammar covers those samples was
wrong.

- Delete the call and its imports.
- State the grammar's real coverage: prose fences only, via `langs`. Both API
  reference paths are unreachable — samples are JSON, and the cURL usage tabs
  highlight client-side off fumadocs' own factory.
- Correct `code-block.tsx`'s TSDoc, which still said API samples come from
  fumadocs' own renderer. They come through this component; `UsageTab` is the
  renderer that bypasses it.
- Re-home a comment orphaned when two CSS rules merged — it had drifted onto
  the rule below and read as documenting it.
- Drop a `.nd-copy-ignore` claim about transformers emitting those nodes;
  nothing here does, and upstream parity is the reason the clone exists.

apps/docs/components/ui/api-example-selector.tsx

@@ -2,8 +2,14 @@
 
 import type { ComponentProps } from 'react'
 import { useId } from 'react'
-import { chipFieldSurfaceClass, chipFieldTextClass, chipHoverSurfaceClass, cn } from '@sim/emcn'
-import { ChevronDown } from '@sim/emcn/icons'
+import {
+  ChipChevronDown,
+  chipFieldSurfaceClass,
+  chipFieldTextClass,
+  chipGeometryClass,
+  chipHoverSurfaceClass,
+  cn,
+} from '@sim/emcn'
 import type { APIPageClientOptions } from 'fumadocs-openapi/ui/client'
 
 type FumadocsAPIExampleSelector = NonNullable<
@@ -35,10 +41,11 @@ export function APIExampleSelector({ items, value, onValueChange }: APIExampleSe
            * screen-reader behavior a custom listbox would have to rebuild.
            */
           className={cn(
+            chipGeometryClass,
             chipFieldSurfaceClass,
             chipFieldTextClass,
             chipHoverSurfaceClass,
-            'h-[30px] w-full appearance-none ps-2 pe-8 text-left'
+            'w-full appearance-none pe-8'
           )}
         >
           {items.map((item) => (
@@ -47,7 +54,7 @@ export function APIExampleSelector({ items, value, onValueChange }: APIExampleSe
             </option>
           ))}
         </select>
-        <ChevronDown className='-translate-y-1/2 pointer-events-none absolute end-2 top-1/2 size-[14px] text-[var(--text-icon)]' />
+        <ChipChevronDown className='-translate-y-1/2 pointer-events-none absolute end-2 top-1/2' />
       </div>
       {selectedItem?.description && (
         <p className='text-[var(--text-muted)] text-caption'>{selectedItem.description}</p>

apps/docs/components/ui/code-block.tsx

@@ -33,21 +33,24 @@ function CopyButton({ getCode }: { getCode: () => string }) {
 }
 
 /**
- * Docs code block for prose fences, wired into the MDX `pre` mapping.
+ * Docs code block for prose fences and the API reference's request/response samples — the MDX
+ * `pre` mapping and fumadocs-openapi's `renderCodeBlock` both render it.
  *
- * The shell — radius, hairline, fill — is not set here. Request and response samples in the
- * API reference come from fumadocs-openapi's own renderer, so the two share chrome through a
- * `figure.shiki` rule in `global.css` instead; see the note there. What stays here is the
- * part only this path has: the copy control, and the `my-4` prose rhythm that API samples,
- * which sit flush in their panel, must not inherit.
+ * The shell — radius, hairline, fill — is not set here. A third renderer, fumadocs-openapi's
+ * `UsageTab`, emits these figures without going through any component, so all three share
+ * chrome through a `figure.shiki` rule in `global.css` instead; see the note there. What stays
+ * here is the copy control, and the `my-4` prose rhythm that API samples, which sit flush in
+ * their panel, override with `my-0`.
  */
 export function CodeBlock({ title, ...props }: React.ComponentProps<typeof FumadocsCodeBlock>) {
   const figureRef = useRef<HTMLElement>(null)
 
   /**
-   * Reads the block's text the way fumadocs does: from a clone, with `.nd-copy-ignore` nodes
-   * replaced by newlines. Those nodes carry rendered gutter and diff markers, so copying the
-   * live `textContent` would paste line numbers along with the code.
+   * Reads the block's text the way fumadocs' own `CopyButton` does: from a clone, with
+   * `.nd-copy-ignore` nodes replaced by newlines — kept in step with upstream so a fence that
+   * gains such a node copies the same text there and here. (The line-number gutter is a
+   * `::before`, and pseudo-element content never reaches `textContent`, so it is not what this
+   * guards.)
    */
   function getCode() {
     const pre = figureRef.current?.getElementsByTagName('pre').item(0)
@@ -65,8 +68,9 @@ export function CodeBlock({ title, ...props }: React.ComponentProps<typeof Fumad
       className={cn('my-4', props.className)}
       allowCopy={false}
       /**
-       * fumadocs' own `className` is discarded rather than merged — its untitled-block variant
-       * carries a `backdrop-blur-lg` that goes milky over an opaque fill.
+       * The `className` fumadocs passes this render prop is deliberately neither destructured nor
+       * merged — its untitled-block variant carries a `backdrop-blur-lg` that goes milky over an
+       * opaque fill.
        */
       Actions={() => (
         <div className={cn('flex items-center', title ? '-me-1' : 'absolute top-2 right-2 z-[1]')}>