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

snake/loop.go

@@ -62,7 +62,7 @@ func (si *SnakeGameInstance) countdownPhase() {
 				si.game.Status = StatusInProgress
 
 				if si.queries != nil {
-					si.saveSnakeGame(si.game)
+					si.saveSnakeGame(si.game) //nolint:errcheck
 				}
 				si.gameMu.Unlock()
 				si.notify()
@@ -70,7 +70,7 @@ func (si *SnakeGameInstance) countdownPhase() {
 			}
 
 			if si.queries != nil {
-				si.saveSnakeGame(si.game)
+				si.saveSnakeGame(si.game) //nolint:errcheck
 			}
 			si.gameMu.Unlock()
 			si.notify()
@@ -124,7 +124,7 @@ func (si *SnakeGameInstance) gamePhase() {
 			if time.Since(lastInput) > inactivityLimit {
 				si.game.Status = StatusFinished
 				if si.queries != nil {
-					si.saveSnakeGame(si.game)
+					si.saveSnakeGame(si.game) //nolint:errcheck
 				}
 				si.gameMu.Unlock()
 				si.notify()
@@ -196,7 +196,7 @@ func (si *SnakeGameInstance) gamePhase() {
 			}
 
 			if si.queries != nil {
-				si.saveSnakeGame(si.game)
+				si.saveSnakeGame(si.game) //nolint:errcheck
 			}
 
 			si.gameMu.Unlock()