feat(cli): add admin REPL + commands and docs

- Add CLI entry in backend with default REPL, persistent history, aliases
- Add commands: users:list/create/verify, events:list/details/participants/checkin,
  matches:list, logs:app, logs:messages
- Support running subcommands inside REPL via .cli and run()
- Add Makefile targets: dev-cli, prod-cli, dev/prod up/down (+rebuild)
- Update README and add docs/ADMIN_CLI.md
- Add CLI tests with mocked Prisma

backend/package.json

@@ -11,7 +11,8 @@
     "prisma:generate": "prisma generate",
     "prisma:migrate": "prisma migrate dev",
     "prisma:seed": "node prisma/seed.js",
-    "prisma:studio": "prisma studio"
+    "prisma:studio": "prisma studio",
+    "cli": "node src/cli/index.js"
   },
   "keywords": [
     "webrtc",