feat: rewrite as moderation bot (#11)

## Summary

- Replaces the old AI companion bot with a full Discord moderation system
- Adds 8 slash commands: `warn`, `mute`, `unmute`, `kick`, `softban`, `ban`, `unban`, `prune`
- Adds logging for member join/leave, activity (messages, threads, voice), and moderation actions
- Audit log integration captures manual bans, kicks, timeouts, and unbans
- All applicable actions post sanctions to the Hikari sanction API
- All commands are ephemeral, use Components v2, and enforce permission + role hierarchy checks

## Test plan

- [ ] Run `pnpm register` to register all 8 commands to the guild
- [ ] Verify each command appears in Discord and is only visible to members with the appropriate permissions
- [ ] Test each command against a valid target and confirm mod log entry, DM notification, and sanction record
- [ ] Test each command against an invalid target (equal/higher role, self, bot) and confirm correct error response
- [ ] Perform a manual ban, kick, and timeout in the Discord UI and confirm audit log handler picks them up
- [ ] Perform a manual unban and confirm it logs correctly without creating a sanction
- [ ] Verify join/leave messages appear in the welcome log channel
- [ ] Verify message edits, deletes, thread events, and voice state changes appear in the activity log channel

✨ This issue was created with help from Hikari~ 🌸

Reviewed-on: #11
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

src/events/messageDelete.ts

@@ -0,0 +1,69 @@
+/**
+ * @copyright nhcarrigan
+ * @license Naomi's Public License
+ * @author Naomi Carrigan
+ */
+
+import { logActivity } from "../modules/logActivity.js";
+import { logger } from "../utils/logger.js";
+import type { Message, PartialMessage } from "discord.js";
+
+/**
+ * Resolves the displayable content for a deleted message.
+ * @param rawContent - The raw message content, which may be null if uncached.
+ * @returns A displayable string representation of the content.
+ */
+const resolveContent = (rawContent: string | null): string => {
+  if (rawContent === null || rawContent === "") {
+    return "*Not cached*";
+  }
+
+  if (rawContent.length > 1024) {
+    return `${rawContent.slice(0, 1021)}...`;
+  }
+
+  return rawContent;
+};
+
+/**
+ * Logs message deletion events to the activity log channel.
+ * Content is only available if the message was cached prior to deletion.
+ * @param message - The deleted message (may be partial if uncached).
+ * @returns A promise that resolves when the event has been logged.
+ */
+export const onMessageDelete = async(
+  message: Message | PartialMessage,
+): Promise<void> => {
+  if (message.author?.bot === true) {
+    return;
+  }
+
+  if (!message.guild) {
+    return;
+  }
+
+  try {
+    const content = resolveContent(message.content);
+
+    const fields = [
+      `**Channel**: <#${message.channelId}>`,
+      `**Message ID**: \`${message.id}\``,
+      `**Author**: ${message.author?.username ?? "Unknown"} (\`${message.author?.id ?? "Unknown"}\`)`,
+      `**Content**: ${content}`,
+    ].join("\n");
+
+    await logActivity({
+      client: message.client,
+      emoji:  "🗑️",
+      fields: fields,
+      title:  "Message Deleted",
+    });
+  } catch (error) {
+    await logger.error(
+      "Failed to log message delete",
+      error instanceof Error
+        ? error
+        : new Error(String(error)),
+    );
+  }
+};