refactor: convert ModerationService and PruneService from classes to singleton objects

- Convert ModerationService class to moderationService singleton
- Convert PruneService class to pruneService singleton
- Update all command files to use new singleton imports
- Update web routes to use new singleton imports
- Update tests for singleton pattern
- Remove getNextCaseId from tests (now private module function)

bot/commands/admin/warn.ts

@@ -1,6 +1,6 @@
 import { createCommand } from "@shared/lib/utils";
 import { SlashCommandBuilder, PermissionFlagsBits, MessageFlags } from "discord.js";
-import { ModerationService } from "@shared/modules/moderation/moderation.service";
+import { moderationService } from "@shared/modules/moderation/moderation.service";
 import {
     getWarnSuccessEmbed,
     getModerationErrorEmbed,
@@ -54,7 +54,7 @@ export const warn = createCommand({
             const guildConfig = await getGuildConfig(interaction.guildId!);
 
             // Issue the warning via service
-            const { moderationCase, warningCount, autoTimeoutIssued } = await ModerationService.issueWarning({
+            const { moderationCase, warningCount, autoTimeoutIssued } = await moderationService.issueWarning({
                 userId: targetUser.id,
                 username: targetUser.username,
                 moderatorId: interaction.user.id,