refactor(bot): remove old Express/EJS admin panel, add standalone health server (v1.2.7)

- Delete src/admin/ (1012 files: routes, views, public, auth) — old admin replaced by Next.js admin-next/
- Add src/healthServer.js: minimal HTTP /health on port 3001 for Docker healthcheck
- src/index.js uses startHealthServer instead of startAdminPanel
- Remove admin-dependent test (adminDeleteFeedback.test.js); 30 tests pass
- Remove ejs/express-ejs-layouts/express/cookie-parser/multer from deps
- admin-next: prisma binaryTargets for linux-arm64-openssl (arm64 prod)
- VERSION.md v1.2.7
- Bot adminHandlers (Telegram commands) kept — data preserved in shared SQLite

admin-next/prisma/schema.prisma

@@ -1,5 +1,6 @@
 generator client {
   provider = "prisma-client-js"
+  binaryTargets = ["native", "linux-arm64-openssl-3.0.x", "linux-arm64-openssl-1.1.x", "linux-arm64-openssl-1.0.x"]
 }
 
 datasource db {