fix: comprehensive bug fixes and architecture restructuring

Phase 1 — Bug fixes (7 bugs):
- Bug 1: Pulsar mode data loss — always persist to SQLite regardless of mode
- Bug 2: PulsarSend closing TCP client — use independent resetPulsarProducer()
- Bug 3: Greedy regex — use non-greedy (?s)ZCZC.*?NNNN
- Bug 4: Data after NNNN discarded — keep remaining buffer data
- Bug 5: strings.Index > 0 boundary — use strings.Contains
- Bug 6: Variable shadowing in PulsarSend — use = not :=
- Bug 7: Accept failure nil panic — add continue + retry logic

Phase 2 — Architecture restructuring:
- Split utils/ into config/, serial/, telegram/, storage/, transport/
- Define Sender, Repository, Reader interfaces
- Introduce app/ layer with context.Context lifecycle
- Replace spinlock with sync.Mutex
- Unified Config struct replaces 15+ global vars

Phase 3 — Testing & tooling:
- telegram/parser_test.go (7 test cases)
- storage/store_test.go (5 test cases)
- transport/transport_test.go (4 test cases)
- Taskfile: add test, test-race, test-cover tasks
- Go version: 1.15 -> 1.21

config/loader.go

@@ -0,0 +1,54 @@
+package config
+
+import (
+	"github.com/spf13/viper"
+)
+
+// Load reads configuration from telegram.yaml using viper.
+func Load(path string) (*Config, error) {
+	v := viper.New()
+
+	if path != "" {
+		v.SetConfigFile(path)
+	} else {
+		v.AddConfigPath(".")
+		v.SetConfigName("telegram")
+	}
+
+	v.AutomaticEnv()
+
+	if err := v.ReadInConfig(); err != nil {
+		return nil, err
+	}
+
+	cfg := &Config{
+		Serial: SerialConfig{
+			Device:   v.GetString("serial.device"),
+			Baudrate: v.GetInt("serial.baudrate"),
+			LogRaw:   v.GetBool("serial.lograw"),
+		},
+		Telegram: TelegramConfig{
+			TCP:    v.GetBool("telegram.tcp"),
+			Pulsar: v.GetBool("telegram.pulsar"),
+		},
+		SQLite: SQLiteConfig{
+			File: v.GetString("sqlite.file"),
+			Init: v.GetBool("sqlite.init"),
+		},
+		Socket: SocketConfig{
+			Address: v.GetString("socket.address"),
+		},
+		Pulsar: PulsarConfig{
+			URL:   v.GetString("pulsar.url"),
+			Topic: v.GetString("pulsar.topic"),
+			Name:  v.GetString("pulsar.name"),
+		},
+		Log: LogConfig{
+			Dir:        "./logs",
+			MaxAge:     60,
+			RotateHour: 1,
+		},
+	}
+
+	return cfg, nil
+}