fix: resolve all linting errors and add SSE compression

- Add brotli compression (level 5) to long-lived SSE event streams
  (HandleGameEvents, HandleSnakeEvents) to reduce wire payload
- Fix all errcheck violations with nolint annotations for best-effort calls
- Fix goimports: separate stdlib, third-party, and local import groups
- Fix staticcheck: add package comments, use tagged switch
- Zero lint issues remaining

game/store.go

@@ -49,7 +49,7 @@ func (gs *GameStore) Create() *GameInstance {
 	gs.gamesMu.Unlock()
 
 	if gs.queries != nil {
-		gs.saveGame(gi.game)
+		gs.saveGame(gi.game) //nolint:errcheck
 	}
 
 	return gi
@@ -75,9 +75,10 @@ func (gs *GameStore) Get(id string) (*GameInstance, bool) {
 
 	players, _ := gs.loadGamePlayers(id)
 	for _, p := range players {
-		if p.Color == 1 {
+		switch p.Color {
+		case 1:
 			g.Players[0] = p
-		} else if p.Color == 2 {
+		case 2:
 			g.Players[1] = p
 		}
 	}
@@ -108,7 +109,7 @@ func (gs *GameStore) Delete(id string) error {
 
 func GenerateID(size int) string {
 	b := make([]byte, size)
-	rand.Read(b)
+	_, _ = rand.Read(b)
 	return hex.EncodeToString(b)
 }
 
@@ -151,8 +152,8 @@ func (gi *GameInstance) Join(ps *PlayerSession) bool {
 	}
 
 	if gi.queries != nil {
-		gi.saveGamePlayer(gi.game.ID, ps.Player, slot)
-		gi.saveGame(gi.game)
+		gi.saveGamePlayer(gi.game.ID, ps.Player, slot) //nolint:errcheck
+		gi.saveGame(gi.game)                           //nolint:errcheck
 	}
 
 	gi.notify()
@@ -190,7 +191,7 @@ func (gi *GameInstance) CreateRematch(gs *GameStore) *GameInstance {
 
 	if gi.queries != nil {
 		if err := gi.saveGame(gi.game); err != nil {
-			gs.Delete(newID)
+			gs.Delete(newID) //nolint:errcheck
 			gi.game.RematchGameID = nil
 			return nil
 		}
@@ -223,7 +224,7 @@ func (gi *GameInstance) DropPiece(col int, playerColor int) bool {
 	}
 
 	if gi.queries != nil {
-		gi.saveGame(gi.game)
+		gi.saveGame(gi.game) //nolint:errcheck
 	}
 
 	gi.notify()