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

storage/store_test.go

@@ -2,6 +2,7 @@ package storage
 
 import (
 	"os"
+	"sync"
 	"testing"
 )
 
@@ -95,3 +96,99 @@ func TestStore_Empty(t *testing.T) {
 		t.Errorf("expected 0 telegrams, got %d", len(telegrams))
 	}
 }
+
+func TestStore_ConcurrentInsert(t *testing.T) {
+	dbFile := "test_concurrent.db"
+	defer os.Remove(dbFile)
+
+	s, err := New(dbFile, true)
+	if err != nil {
+		t.Fatalf("New() failed: %v", err)
+	}
+	defer s.Close()
+
+	var wg sync.WaitGroup
+	const numGoroutines = 10
+	const insertsPerGoroutine = 10
+
+	for i := 0; i < numGoroutines; i++ {
+		wg.Add(1)
+		go func(id int) {
+			defer wg.Done()
+			for j := 0; j < insertsPerGoroutine; j++ {
+				telegram := "ZCZC CONCURRENT MSG"
+				if err := s.Insert(telegram); err != nil {
+					t.Errorf("concurrent Insert() failed: %v", err)
+				}
+			}
+		}(i)
+	}
+	wg.Wait()
+
+	count, err := s.CountUnprocessed()
+	if err != nil {
+		t.Fatalf("CountUnprocessed() after concurrent inserts failed: %v", err)
+	}
+	expected := int64(numGoroutines * insertsPerGoroutine)
+	if count != expected {
+		t.Errorf("expected %d unprocessed, got %d", expected, count)
+	}
+}
+
+func TestStore_CloseAndReopen(t *testing.T) {
+	dbFile := "test_reopen.db"
+	defer os.Remove(dbFile)
+
+	// Create and insert
+	s, err := New(dbFile, true)
+	if err != nil {
+		t.Fatalf("New() failed: %v", err)
+	}
+	if err := s.Insert("ZCZC PERSIST NNNN"); err != nil {
+		t.Fatalf("Insert() failed: %v", err)
+	}
+	s.Close()
+
+	// Reopen without init flag
+	s2, err := New(dbFile, false)
+	if err != nil {
+		t.Fatalf("New() reopen failed: %v", err)
+	}
+	defer s2.Close()
+
+	count, err := s2.CountUnprocessed()
+	if err != nil {
+		t.Fatalf("CountUnprocessed() on reopened db failed: %v", err)
+	}
+	if count != 1 {
+		t.Errorf("expected 1 unprocessed after reopen, got %d", count)
+	}
+}
+
+func TestStore_InitClearsDatabase(t *testing.T) {
+	dbFile := "test_init_clear.db"
+	defer os.Remove(dbFile)
+
+	// Create and insert
+	s, err := New(dbFile, false)
+	if err != nil {
+		t.Fatalf("New() failed: %v", err)
+	}
+	s.Insert("ZCZC WILL BE CLEARED NNNN")
+	s.Close()
+
+	// Reopen with init=true (should recreate)
+	s2, err := New(dbFile, true)
+	if err != nil {
+		t.Fatalf("New() with init=true failed: %v", err)
+	}
+	defer s2.Close()
+
+	count, err := s2.CountUnprocessed()
+	if err != nil {
+		t.Fatalf("CountUnprocessed() failed: %v", err)
+	}
+	if count != 0 {
+		t.Errorf("expected 0 unprocessed after init, got %d", count)
+	}
+}