webui: Fix branching logic on edit message (#21175)

* fix: Branching logic + small refactor

* chore: update webui build output

tools/server/webui/src/lib/utils/branching.ts

@@ -17,6 +17,17 @@
 
 import { MessageRole } from '$lib/enums';
 
+/**
+ * Finds a message by its ID in the given messages array.
+ */
+export function findMessageById(
+	messages: readonly DatabaseMessage[],
+	id: string | null | undefined
+): DatabaseMessage | undefined {
+	if (!id) return undefined;
+	return messages.find((m) => m.id === id);
+}
+
 /**
  * Filters messages to get the conversation path from root to a specific leaf node.
  * If the leafNodeId doesn't exist, returns the path with the latest timestamp.