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/threadUpdate.ts

@@ -0,0 +1,67 @@
+/**
+ * @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 */
+
+import { logActivity } from "../modules/logActivity.js";
+import { logger } from "../utils/logger.js";
+import type { AnyThreadChannel } from "discord.js";
+
+/**
+ * Logs thread update events to the activity log channel.
+ * Only logs when the thread name changes to avoid noise from archive state changes.
+ * @param oldThread - The thread state before the update.
+ * @param newThread - The thread state after the update.
+ * @returns A promise that resolves when the event has been logged.
+ */
+export const onThreadUpdate = async(
+  oldThread: AnyThreadChannel,
+  newThread: AnyThreadChannel,
+): Promise<void> => {
+  if (
+    oldThread.name === newThread.name
+    && oldThread.archived === newThread.archived
+  ) {
+    return;
+  }
+
+  try {
+    const changes: Array<string> = [];
+
+    if (oldThread.name !== newThread.name) {
+      changes.push(`**Name**: \`${oldThread.name}\` → \`${newThread.name}\``);
+    }
+
+    if (oldThread.archived !== newThread.archived) {
+      const wasArchived = oldThread.archived === true
+        ? "Yes"
+        : "No";
+      const isArchived = newThread.archived === true
+        ? "Yes"
+        : "No";
+      changes.push(`**Archived**: ${wasArchived} → ${isArchived}`);
+    }
+
+    const fields = [
+      `**Thread**: ${newThread.name} (\`${newThread.id}\`)`,
+      `**Parent**: <#${newThread.parentId ?? "Unknown"}>`,
+      ...changes,
+    ].join("\n");
+
+    await logActivity({
+      client: newThread.client,
+      emoji:  "🔄",
+      fields: fields,
+      title:  "Thread Updated",
+    });
+  } catch (error) {
+    await logger.error(
+      "Failed to log thread update",
+      error instanceof Error
+        ? error
+        : new Error(String(error)),
+    );
+  }
+};