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

telegram/parser.go

@@ -0,0 +1,83 @@
+package telegram
+
+import (
+	"io"
+	"regexp"
+	"strings"
+	"sync"
+)
+
+const (
+	endTag         = "NNNN"
+	expression     = "(?s)ZCZC.*?NNNN"
+	maxBufferSize  = 65536
+	bufferTrimSize = 32768
+)
+
+// Parser handles telegram extraction from raw serial data.
+type Parser struct {
+	mu     sync.Mutex
+	buffer strings.Builder
+	exp    *regexp.Regexp
+	rawLog io.Writer
+}
+
+// New creates a new Parser.
+func New(rawLog io.Writer) *Parser {
+	return &Parser{
+		exp:    regexp.MustCompile(expression),
+		rawLog: rawLog,
+	}
+}
+
+// Append adds raw data to the internal buffer and returns any complete
+// telegrams that were found. Returns nil if no complete telegram is ready.
+func (p *Parser) Append(data string) []string {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	if p.buffer.Len() > maxBufferSize {
+		// Truncate to prevent unbounded growth
+		existing := p.buffer.String()
+		p.buffer.Reset()
+		p.buffer.WriteString(existing[len(existing)-bufferTrimSize:])
+	}
+
+	p.buffer.WriteString(data)
+	p.buffer.WriteByte('\n')
+
+	return p.extract()
+}
+
+// extract finds and returns all complete telegrams in the buffer.
+func (p *Parser) extract() []string {
+	content := p.buffer.String()
+
+	if !strings.Contains(content, endTag) {
+		return nil
+	}
+
+	loc := p.exp.FindStringIndex(content)
+	if loc == nil {
+		return nil
+	}
+
+	telegram := content[loc[0]:loc[1]]
+	telegram = removeEmpty(telegram) + "\n\n\n"
+
+	// Write raw log
+	if p.rawLog != nil {
+		p.rawLog.Write([]byte(telegram + "\n"))
+	}
+
+	// Keep remaining data after the matched telegram
+	remaining := content[loc[1]:]
+	p.buffer.Reset()
+	p.buffer.WriteString(remaining)
+
+	return []string{telegram}
+}
+
+func removeEmpty(s string) string {
+	return regexp.MustCompile(`[\t\r\n]+`).ReplaceAllString(strings.TrimSpace(s), "\n")
+}