Adds tools.go to pin protoc-gen-go, updates go.mod/go.sum with
google.golang.org/protobuf, generates request.pb.go and response.pb.go,
and adds a make proto target to server/Makefile for regen.
Remove 3,612 lines of card game implementations (Dou Dizhu, Texas
Hold'em, Mahjong, Uno, Liar's Bar, Run Fast), their database models,
rule engine, skill system, and render package.
Simplify Room struct by removing card-game-specific fields, clean up
consts to only gomoku game type, and remove unused dependencies
(mahjong, uno, cast, color).
Import source files from ratel-online organization repos into monorepo
structure for gomoku game development. Update README with project
structure and credits for original authors.