fix: inherit custom media renderer in nested RichText components

Previously, nested RichText components (like those in QuotedEvent/KindRenderer)
would always reset the media renderer context to null because the provider
used `renderMedia ?? null`. This caused embedded events in chat to use
the default media renderer instead of ChatMediaRenderer.

Now RichText inherits the parent media renderer when no explicit renderMedia
prop is passed, allowing custom renderers to work throughout the entire
rich text subtree including quoted events.

https://claude.ai/code/session_01AeeN5d5EcVLGjZbGueZxaD

src/components/nostr/RichText.tsx

@@ -146,6 +146,9 @@ export function RichText({
   renderMedia,
   children,
 }: RichTextProps) {
+  // Get parent media renderer to inherit if not explicitly overridden
+  const parentMediaRenderer = useMediaRenderer();
+
   // Merge provided options with defaults
   const mergedOptions: Required<RichTextOptions> = {
     ...defaultOptions,
@@ -191,7 +194,9 @@ export function RichText({
   return (
     <DepthContext.Provider value={depth}>
       <OptionsContext.Provider value={mergedOptions}>
-        <MediaRendererContext.Provider value={renderMedia ?? null}>
+        <MediaRendererContext.Provider
+          value={renderMedia !== undefined ? renderMedia : parentMediaRenderer}
+        >
           <EventContext.Provider value={event ?? null}>
             <div
               dir="auto"