Refactor: extract emoji shortcode regex to constant

Move the emoji shortcode matching pattern to EMOJI_SHORTCODE_REGEX
constant in emoji-helpers.ts for reuse across reaction renderers.

src/components/nostr/compact/ReactionCompactPreview.tsx

@@ -4,6 +4,7 @@ import { Heart, ThumbsUp, ThumbsDown, Flame, Smile } from "lucide-react";
 import { useNostrEvent } from "@/hooks/useNostrEvent";
 import { UserName } from "../UserName";
 import { RichText } from "../RichText";
+import { EMOJI_SHORTCODE_REGEX } from "@/lib/emoji-helpers";
 
 /**
  * Compact preview for Kind 7 (Reaction)
@@ -26,7 +27,7 @@ export function ReactionCompactPreview({ event }: { event: NostrEvent }) {
 
   // Parse reaction content for custom emoji
   const parsedReaction = useMemo(() => {
-    const match = reaction.match(/^:([a-zA-Z0-9_-]+):$/);
+    const match = reaction.match(EMOJI_SHORTCODE_REGEX);
     if (match && customEmojis[match[1]]) {
       return {
         type: "custom" as const,

src/components/nostr/kinds/ReactionRenderer.tsx

@@ -6,6 +6,7 @@ import { NostrEvent } from "@/types/nostr";
 import { KindRenderer } from "./index";
 import { EventCardSkeleton } from "@/components/ui/skeleton";
 import { parseReplaceableAddress } from "applesauce-core/helpers/pointers";
+import { EMOJI_SHORTCODE_REGEX } from "@/lib/emoji-helpers";
 
 /**
  * Renderer for Kind 7 - Reactions
@@ -32,7 +33,7 @@ export function Kind7Renderer({ event }: BaseEventProps) {
   // Parse reaction content to detect custom emoji shortcodes
   // Format: :shortcode: in the content
   const parsedReaction = useMemo(() => {
-    const match = reaction.match(/^:([a-zA-Z0-9_-]+):$/);
+    const match = reaction.match(EMOJI_SHORTCODE_REGEX);
     if (match && customEmojis[match[1]]) {
       return {
         type: "custom" as const,

src/lib/emoji-helpers.ts

@@ -1,6 +1,12 @@
 import { getOrComputeCachedValue } from "applesauce-core/helpers";
 import type { NostrEvent } from "@/types/nostr";
 
+/**
+ * Regex pattern to match NIP-30 custom emoji shortcodes like :shortcode:
+ * Supports alphanumeric characters, underscores, and dashes
+ */
+export const EMOJI_SHORTCODE_REGEX = /^:([a-zA-Z0-9_-]+):$/;
+
 /**
  * Represents a parsed emoji tag from NIP-30
  */