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

biome.json

@@ -11,13 +11,11 @@
       "tests/**/*.ts",
       "services/**/*.ts",
       "services/**/*.tsx",
-      "packages/**/*.ts",
       "*.json",
       "*.ts",
       "!vendor",
       "!.claude",
       "!services/**/dist",
-      "!packages/**/dist",
       "!services/**/.next",
       "!services/**/out"
     ]