Create simple/standard validation for network messages

• All packets should check against required payload fields
• name should impose a min/max length (0-20?)
• avatar should impose payload size limits and ensure only known keyframes are specified (basically a deep validation against the JSON schema)
• auth needs to validate the chosen room against something (at a minimum, the characters to use and string length). Moreso a decision needs to be made as to how rooms are defined/limited by servers (this'll be in another ticket)
• move needs to validate buffer format, and check buffer against our desired coordinates within some error tolerance
• say needs to limit message length and optionally do word filtering (will decide later how this works, but a much lower priority)

Start by locating the server's packet/message handling and the payload definitions for name, avatar, auth, move, and say. Define the validation rules and schema boundaries first; done means every listed message has required-field, length, size, format, and coordinate checks, with unresolved room and filtering decisions explicitly settled.