fix: adapt code to modernized libraries

- Migrate validation.ts from class-transformer/class-validator to Zod
- Apply Biome auto-fixes (import sorting, nodejs protocol)
- Fix duplicate type identifier in validation.ts

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/moderation/messageCapture.ts

@@ -34,9 +34,9 @@ export async function captureMessage(
     guild_id: message.guildId!,
     channel_id: location.channelId,
     thread_id: location.threadId,
-    user_id: message.author!.id,
-    username: message.author!.username,
-    avatar_url: message.author!.avatarURL() || null,
+    user_id: message.author?.id,
+    username: message.author?.username,
+    avatar_url: message.author?.avatarURL() || null,
     content: getDisplayContent(message),
     edited_content: null,
     created_at: message.createdTimestamp,
@@ -67,7 +67,7 @@ export async function captureMessage(
         guild_id: message.guildId!,
         channel_id: location.channelId,
         thread_id: location.threadId,
-        user_id: message.author!.id,
+        user_id: message.author?.id,
         filename: attachment.name || "unknown",
         size: attachment.size,
         type: attachment.contentType || "application/octet-stream",