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

storage/store.go

@@ -0,0 +1,131 @@
+package storage
+
+import (
+	"database/sql"
+	"os"
+	"sync"
+
+	_ "github.com/mattn/go-sqlite3"
+)
+
+// Repository defines the interface for telegram persistence.
+type Repository interface {
+	Insert(telegram string) error
+	LoadUnprocessed() ([]Telegram, error)
+	MarkProcessed(id int64) error
+	Close() error
+}
+
+// Telegram represents a stored telegram record.
+type Telegram struct {
+	ID   int64
+	Text string
+}
+
+// Store implements Repository using SQLite.
+type Store struct {
+	mu         sync.Mutex
+	dbFile     string
+	db         *sql.DB
+	initTable  bool
+}
+
+const (
+	driverName = "sqlite3"
+	tableDDL   = `
+		create table IF NOT EXISTS telegram (
+			[tele_id] INTEGER PRIMARY KEY AUTOINCREMENT,
+			[tele_recv_time] TIMESTAMP NOT NULL DEFAULT (datetime('now', 'localtime')),
+			[tele_processed] int(1) NOT NULL DEFAULT 0,
+			[tele_text] TEXT NOT NULL
+		)
+	`
+	insertSQL = "insert into telegram (tele_text) values (?)"
+	countSQL  = "select count(*) from telegram where tele_processed=0"
+	loadSQL   = "select tele_id, tele_text from telegram where tele_processed=0 Limit 100"
+	updateSQL = "update telegram set tele_processed = 1 where tele_id=?"
+)
+
+// New opens or creates a SQLite store.
+func New(dbFile string, init bool) (*Store, error) {
+	if init {
+		os.Remove(dbFile)
+	}
+
+	db, err := sql.Open(driverName, dbFile)
+	if err != nil {
+		return nil, err
+	}
+
+	if _, err := db.Exec(tableDDL); err != nil {
+		db.Close()
+		return nil, err
+	}
+
+	return &Store{
+		dbFile:    dbFile,
+		db:        db,
+		initTable: init,
+	}, nil
+}
+
+// Insert saves a telegram to the database.
+func (s *Store) Insert(telegram string) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	stmt, err := s.db.Prepare(insertSQL)
+	if err != nil {
+		return err
+	}
+	defer stmt.Close()
+
+	_, err = stmt.Exec(telegram)
+	return err
+}
+
+// LoadUnprocessed returns up to 100 unprocessed telegrams.
+func (s *Store) LoadUnprocessed() ([]Telegram, error) {
+	rows, err := s.db.Query(loadSQL)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var telegrams []Telegram
+	for rows.Next() {
+		var t Telegram
+		if err := rows.Scan(&t.ID, &t.Text); err != nil {
+			return nil, err
+		}
+		telegrams = append(telegrams, t)
+	}
+	return telegrams, nil
+}
+
+// MarkProcessed marks a telegram as processed.
+func (s *Store) MarkProcessed(id int64) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	stmt, err := s.db.Prepare(updateSQL)
+	if err != nil {
+		return err
+	}
+	defer stmt.Close()
+
+	_, err = stmt.Exec(id)
+	return err
+}
+
+// CountUnprocessed returns the number of unprocessed telegrams.
+func (s *Store) CountUnprocessed() (int64, error) {
+	var count int64
+	err := s.db.QueryRow(countSQL).Scan(&count)
+	return count, err
+}
+
+// Close closes the database connection.
+func (s *Store) Close() error {
+	return s.db.Close()
+}