Remove dead and mismatched dependencies

A cleanup pass over package.json in both workspaces:

• axios + @types/axios (frontend): installed, never imported anywhere
• @types/socket.io and @types/socket.io-client: deprecated stub packages, both libraries ship their own types
• @types/bcryptjs: bcryptjs v3 ships its own types
• cross-env (backend): no script uses it
• node-mocks-http (backend): sitting in production dependencies, unused in src
• @types/express is v5 while express is v4, so the types don't match the runtime. Pin to @types/express@4 until the Hono migration removes express entirely

Check each with a grep before deleting, then verify build + tests still pass.