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

serial/serial.go

@@ -0,0 +1,50 @@
+package serial
+
+import (
+	"time"
+
+	"github.com/argandas/serial"
+)
+
+// Reader defines the interface for serial port operations.
+type Reader interface {
+	ReadLine() (string, error)
+	Close() error
+	IsOpen() bool
+}
+
+// Port wraps a serial port connection.
+type Port struct {
+	sp     *serial.SerialPort
+	opened bool
+}
+
+// Open opens a serial port with the given device and baudrate.
+func Open(device string, baudrate int) (*Port, error) {
+	sp := serial.New()
+	sp.EOL('\r')
+	sp.Verbose = false
+
+	err := sp.Open(device, baudrate, 3*time.Second)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Port{sp: sp, opened: true}, nil
+}
+
+// ReadLine reads one line from the serial port.
+func (p *Port) ReadLine() (string, error) {
+	return p.sp.ReadLine()
+}
+
+// Close closes the serial port.
+func (p *Port) Close() error {
+	p.opened = false
+	return nil
+}
+
+// IsOpen returns whether the port is currently open.
+func (p *Port) IsOpen() bool {
+	return p.opened
+}