refactor: break monorepo into 3 standalone services (gateway, backend, frontend)

- Remove pnpm workspace, moon repo, and all monorepo tooling
- Delete packages/shared/, embed shared code directly into each service
- Copy packages/shared/src/* -> services/backend/src/shared/ and services/discord-gateway/src/shared/
- Replace all @bete/shared imports with @/shared/ path alias
- Remove @bete/shared workspace dependency from both services
- Update root package.json scripts from --filter to --prefix
- Rewrite Dockerfiles to build each service standalone
- Clean up biome.json, .gitignore, remove root drizzle.config.ts

services/discord-gateway/src/modules/command-handler/media.handler.ts

@@ -1,6 +1,6 @@
 import { randomUUID } from "node:crypto";
-import type { CommandMessage, CommandReply } from "@bete/shared";
-import { createChildLogger } from "@bete/shared/logger";
+import type { CommandMessage, CommandReply } from "../../shared/index.js";
+import { createChildLogger } from "../../shared/logger/index.js";
 import { StreamType } from "@discordjs/voice";
 import {
   extractMediaInfo,