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

features/lobby/handlers.go

@@ -91,7 +91,7 @@ func HandleCreateGame(store *game.GameStore, sessions *scs.SessionManager) http.
 
 		gi := store.Create()
 		sse := datastar.NewSSE(w, r)
-		sse.ExecuteScript(fmt.Sprintf("window.location.href='/game/%s'", gi.ID()))
+		sse.ExecuteScript(fmt.Sprintf("window.location.href='/game/%s'", gi.ID())) //nolint:errcheck
 	}
 }
 
@@ -104,10 +104,10 @@ func HandleDeleteGame(store *game.GameStore, sessions *scs.SessionManager) http.
 			return
 		}
 
-		store.Delete(gameID)
+		store.Delete(gameID) //nolint:errcheck
 
 		sse := datastar.NewSSE(w, r)
-		sse.ExecuteScript("window.location.href='/'")
+		sse.ExecuteScript("window.location.href='/'") //nolint:errcheck
 	}
 }
 
@@ -150,7 +150,7 @@ func HandleCreateSnakeGame(snakeStore *snake.SnakeStore, sessions *scs.SessionMa
 		si := snakeStore.Create(preset.Width, preset.Height, mode, speed)
 
 		sse := datastar.NewSSE(w, r)
-		sse.ExecuteScript(fmt.Sprintf("window.location.href='/snake/%s'", si.ID()))
+		sse.ExecuteScript(fmt.Sprintf("window.location.href='/snake/%s'", si.ID())) //nolint:errcheck
 	}
 }
 
@@ -163,6 +163,6 @@ func HandleLogout(sessions *scs.SessionManager) http.HandlerFunc {
 		}
 
 		sse := datastar.NewSSE(w, r)
-		sse.ExecuteScript("window.location.href='/'")
+		sse.ExecuteScript("window.location.href='/'") //nolint:errcheck
 	}
 }