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/userUpdate.ts

@@ -0,0 +1,74 @@
+/**
+ * @copyright nhcarrigan
+ * @license Naomi's Public License
+ * @author Naomi Carrigan
+ */
+/* eslint-disable unicorn/no-keyword-prefix -- old/new prefixes are the established Discord.js event parameter names */
+/* eslint-disable max-lines-per-function -- Event handler checks multiple independent change types */
+
+import { logActivity } from "../modules/logActivity.js";
+import { logger } from "../utils/logger.js";
+import type { PartialUser, User } from "discord.js";
+
+/**
+ * Logs user profile update events (username, display name, avatar) to the
+ * activity log channel. Skips bots.
+ * @param oldUser - The user before the update.
+ * @param newUser - The user after the update.
+ * @returns A promise that resolves when all applicable changes have been logged.
+ */
+export const onUserUpdate = async(
+  oldUser: PartialUser | User,
+  newUser: User,
+): Promise<void> => {
+  if (newUser.bot) {
+    return;
+  }
+
+  try {
+    if (oldUser.username !== newUser.username) {
+      await logActivity({
+        client: newUser.client,
+        emoji:  "✏️",
+        fields: [
+          `**User**: ${newUser.username} (\`${newUser.id}\`)`,
+          `**Before**: ${oldUser.username ?? "*(unknown)*"}`,
+          `**After**: ${newUser.username}`,
+        ].join("\n"),
+        title: "Username Changed",
+      });
+    }
+
+    if (oldUser.globalName !== newUser.globalName) {
+      await logActivity({
+        client: newUser.client,
+        emoji:  "📛",
+        fields: [
+          `**User**: ${newUser.username} (\`${newUser.id}\`)`,
+          `**Before**: ${oldUser.globalName ?? "*(none)*"}`,
+          `**After**: ${newUser.globalName ?? "*(none)*"}`,
+        ].join("\n"),
+        title: "Display Name Changed",
+      });
+    }
+
+    if (oldUser.avatar !== newUser.avatar) {
+      await logActivity({
+        client: newUser.client,
+        emoji:  "🖼️",
+        fields: [
+          `**User**: ${newUser.username} (\`${newUser.id}\`)`,
+          `**New Avatar**: ${newUser.displayAvatarURL()}`,
+        ].join("\n"),
+        title: "Avatar Changed",
+      });
+    }
+  } catch (error) {
+    await logger.error(
+      "Failed to log user update",
+      error instanceof Error
+        ? error
+        : new Error(String(error)),
+    );
+  }
+};