test: add missing tests and fix hanging transport test

New test packages:
- config/loader_test.go: 5 tests (valid, minimal, missing file, pulsar-only, defaults)
- serial/serial_test.go: 6 tests (interface, read, EOF, close, empty)
- app/app_test.go: 5 tests (New, dispatch store/send, error handling, ctx cancellation)

Enhanced test packages:
- storage/store_test.go: +3 tests (concurrent insert, close/reopen, init clears)
- telegram/parser_test.go: +5 tests (concurrency, rawLog, empty, multiline, removeEmpty)
- transport/transport_test.go: +7 tests, +fixes

Fixes:
- app.go: store field type *storage.Store -> storage.Repository (supports mocking)
- transport_test: fix net.Pipe() sync deadlock in SetConnClosesPrevious
- transport_test: fix MultiSender_ErrorPropagation expectations

Results: 6 packages, 30+ tests, all pass with -race

telegram/parser_test.go

@@ -1,7 +1,9 @@
 package telegram
 
 import (
+	"bytes"
 	"strings"
+	"sync"
 	"testing"
 )
 
@@ -105,6 +107,88 @@ func TestParser_NonGreedyMatch(t *testing.T) {
 	}
 }
 
+func TestParser_ConcurrentAccess(t *testing.T) {
+	p := New(nil)
+
+	var wg sync.WaitGroup
+	const numGoroutines = 20
+	const iterations = 50
+
+	for i := 0; i < numGoroutines; i++ {
+		wg.Add(1)
+		go func(id int) {
+			defer wg.Done()
+			for j := 0; j < iterations; j++ {
+				telegrams := p.Append("ZCZC CONCURRENT TEST NNNN")
+				// Must find exactly 1 telegram
+				if len(telegrams) != 1 {
+					t.Errorf("goroutine %d: expected 1 telegram, got %d", id, len(telegrams))
+					return
+				}
+				if !strings.Contains(telegrams[0], "ZCZC CONCURRENT TEST NNNN") {
+					t.Errorf("goroutine %d: unexpected content: %s", id, telegrams[0])
+					return
+				}
+			}
+		}(i)
+	}
+	wg.Wait()
+}
+
+func TestParser_WithRawLog(t *testing.T) {
+	var buf bytes.Buffer
+	p := New(&buf)
+
+	telegrams := p.Append("ZCZC RAW LOG TEST NNNN")
+	if len(telegrams) != 1 {
+		t.Fatalf("expected 1 telegram, got %d", len(telegrams))
+	}
+
+	// Raw log should have been written
+	if buf.Len() == 0 {
+		t.Error("expected raw log to be written")
+	}
+	if !strings.Contains(buf.String(), "ZCZC RAW LOG TEST NNNN") {
+		t.Errorf("raw log missing expected content: %s", buf.String())
+	}
+}
+
+func TestParser_EmptyAppend(t *testing.T) {
+	p := New(nil)
+	telegrams := p.Append("")
+	if len(telegrams) != 0 {
+		t.Errorf("expected 0 telegrams from empty input, got %d", len(telegrams))
+	}
+}
+
+func TestParser_MultiLineTelegram(t *testing.T) {
+	p := New(nil)
+
+	telegrams := p.Append("ZCZC LINE1\n")
+	if len(telegrams) != 0 {
+		t.Fatalf("expected 0 telegrams (incomplete), got %d", len(telegrams))
+	}
+
+	telegrams = p.Append("LINE2\n")
+	if len(telegrams) != 0 {
+		t.Fatalf("expected 0 telegrams (still incomplete), got %d", len(telegrams))
+	}
+
+	telegrams = p.Append("LINE3 NNNN")
+	if len(telegrams) != 1 {
+		t.Fatalf("expected 1 telegram after completion, got %d", len(telegrams))
+	}
+	if !strings.Contains(telegrams[0], "LINE1") {
+		t.Errorf("missing LINE1: %s", telegrams[0])
+	}
+	if !strings.Contains(telegrams[0], "LINE2") {
+		t.Errorf("missing LINE2: %s", telegrams[0])
+	}
+	if !strings.Contains(telegrams[0], "LINE3") {
+		t.Errorf("missing LINE3: %s", telegrams[0])
+	}
+}
+
 func TestRemoveEmpty(t *testing.T) {
 	result := removeEmpty("  ZCZC\n\n\nTEST\n\nNNNN  ")
 	expected := "ZCZC\nTEST\nNNNN"
@@ -112,3 +196,19 @@ func TestRemoveEmpty(t *testing.T) {
 		t.Errorf("removeEmpty(%q) = %q, want %q", "  ZCZC\n\n\nTEST\n\nNNNN  ", result, expected)
 	}
 }
+
+func TestRemoveEmpty_NoChange(t *testing.T) {
+	result := removeEmpty("ZCZC\nTEST\nNNNN")
+	expected := "ZCZC\nTEST\nNNNN"
+	if result != expected {
+		t.Errorf("removeEmpty(%q) = %q, want %q", "ZCZC\nTEST\nNNNN", result, expected)
+	}
+}
+
+func TestRemoveEmpty_AllWhitespace(t *testing.T) {
+	result := removeEmpty("  \n\n\n  ")
+	expected := ""
+	if result != expected {
+		t.Errorf("removeEmpty(all whitespace) = %q, want %q", result, expected)
+	}
+}