refactor(grpc): restructure task handling and migrate to slog

Refactor the gRPC client and task handling logic to improve modularity,
error handling, and observability.

- Split `grpc/handler.go` into specialized handler files (login,
  classroom, exams, grades, schedule) to reduce complexity.
- Replace standard `log` with `log/slog` throughout the project for
  structured logging.
- Refactor `grpc/client.go` to use a thread-safe connection management
  pattern with `sync.RWMutex`.
- Remove the legacy `service` package and HTTP server implementation,
  transitioning the application to a pure gRPC runner mode.
- Clean up `config` and `pkg/errors` to remove unused utilities and
  simplify the API.
- Improve error reporting in parsers and HTTP clients by checking
  response status codes.

config/config.go

@@ -1,27 +1,16 @@
 package config
 
 import (
-	"log/slog"
 	"os"
-	"strconv"
 	"sync"
-	"time"
 )
 
 type Config struct {
-	BaseURL    string
-	Username   string
-	Password   string
-	Semester   string
-	TWFID      string
-	Recognizer RecognizerConfig
-}
-
-type RecognizerConfig struct {
-	APIURL  string
-	APIKey  string
-	Model   string
-	Timeout time.Duration
+	BaseURL  string
+	Username string
+	Password string
+	Semester string
+	TWFID    string
 }
 
 var (
@@ -37,16 +26,6 @@ func Load() *Config {
 			Password: getEnv("JWTS_PASSWORD", ""),
 			Semester: getEnv("JWTS_SEMESTER", "2025-20262"),
 			TWFID:    getEnv("JWTS_TWFID", ""),
-			Recognizer: RecognizerConfig{
-				APIURL:  getEnv("RECOGNIZER_API_URL", "https://api.littlelan.cn/v1/chat/completions"),
-				APIKey:  getEnv("RECOGNIZER_API_KEY", ""),
-				Model:   getEnv("RECOGNIZER_MODEL", "qwen3.5-plus"),
-				Timeout: getEnvDuration("RECOGNIZER_TIMEOUT", 120*time.Second),
-			},
-		}
-
-		if cfg.Recognizer.APIKey == "" {
-			slog.Warn("RECOGNIZER_API_KEY not set, image recognition will not work")
 		}
 	})
 	return cfg
@@ -66,36 +45,3 @@ func getEnv(key, defaultValue string) string {
 	}
 	return val
 }
-
-func getEnvInt(key string, defaultValue int) int {
-	val := os.Getenv(key)
-	if val == "" {
-		return defaultValue
-	}
-	if i, err := strconv.Atoi(val); err == nil {
-		return i
-	}
-	return defaultValue
-}
-
-func getEnvDuration(key string, defaultValue time.Duration) time.Duration {
-	val := os.Getenv(key)
-	if val == "" {
-		return defaultValue
-	}
-	if d, err := time.ParseDuration(val); err == nil {
-		return d
-	}
-	return defaultValue
-}
-
-var (
-	BaseURL          = Get().BaseURL
-	Username         = Get().Username
-	Password         = Get().Password
-	Semester         = Get().Semester
-	TWFID            = Get().TWFID
-	RecognizerAPIURL = Get().Recognizer.APIURL
-	RecognizerAPIKey = Get().Recognizer.APIKey
-	RecognizerModel  = Get().Recognizer.Model
-)