feat(PROJ-17): Admin Dashboard Systemauslastung immer anzeigen

- Systemauslastungs-Sektion wird immer gerendert (nicht nur bei Erfolg)
- Fehlermeldung wenn /api/admin/system/stats nicht erreichbar ist
- Feature-Status auf In Review gesetzt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/storage/storage_test.go

@@ -0,0 +1,126 @@
+package storage_test
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/archivmail/internal/storage"
+)
+
+func TestSaveAndLoad(t *testing.T) {
+	dir := t.TempDir()
+	store, err := storage.New(dir)
+	if err != nil {
+		t.Fatalf("New: %v", err)
+	}
+
+	raw := []byte("From: alice@example.com\r\nSubject: Test\r\n\r\nHello World")
+	id, err := store.Save(raw, time.Now())
+	if err != nil {
+		t.Fatalf("Save: %v", err)
+	}
+	if len(id) != 64 {
+		t.Errorf("expected 64-char SHA256 hex, got %d chars", len(id))
+	}
+
+	got, err := store.Load(id)
+	if err != nil {
+		t.Fatalf("Load: %v", err)
+	}
+	if !bytes.Equal(raw, got) {
+		t.Errorf("loaded content mismatch")
+	}
+}
+
+func TestDeduplication(t *testing.T) {
+	dir := t.TempDir()
+	store, err := storage.New(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	raw := []byte("From: alice@example.com\r\n\r\nDuplicate test")
+	id1, err := store.Save(raw, time.Now())
+	if err != nil {
+		t.Fatal(err)
+	}
+	id2, err := store.Save(raw, time.Now())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if id1 != id2 {
+		t.Errorf("duplicate mail produced different IDs: %s vs %s", id1, id2)
+	}
+
+	// Only one file should exist
+	count := 0
+	filepath.Walk(filepath.Join(dir, "store"), func(p string, info os.FileInfo, _ error) error {
+		if !info.IsDir() { count++ }
+		return nil
+	})
+	if count != 1 {
+		t.Errorf("expected 1 stored file after dedup, got %d", count)
+	}
+}
+
+func TestDelete(t *testing.T) {
+	dir := t.TempDir()
+	store, err := storage.New(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	raw := []byte("From: alice@example.com\r\n\r\nDelete me")
+	id, _ := store.Save(raw, time.Now())
+
+	if err := store.Delete(id); err != nil {
+		t.Fatalf("Delete: %v", err)
+	}
+	if _, err := store.Load(id); err == nil {
+		t.Error("Load after Delete should return error")
+	}
+}
+
+func TestStats(t *testing.T) {
+	dir := t.TempDir()
+	store, err := storage.New(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	mails := [][]byte{
+		[]byte("From: a@x.com\r\n\r\nMail 1"),
+		[]byte("From: b@x.com\r\n\r\nMail 2"),
+		[]byte("From: c@x.com\r\n\r\nMail 3"),
+	}
+	for _, m := range mails {
+		store.Save(m, time.Now())
+	}
+
+	stats, err := store.Stats()
+	if err != nil {
+		t.Fatalf("Stats: %v", err)
+	}
+	if stats.TotalMails != 3 {
+		t.Errorf("expected 3 mails, got %d", stats.TotalMails)
+	}
+	if stats.TotalBytes <= 0 {
+		t.Error("expected positive TotalBytes")
+	}
+}
+
+func TestStorageDirectoryCreation(t *testing.T) {
+	dir := filepath.Join(t.TempDir(), "nested", "path")
+	_, err := storage.New(dir)
+	if err != nil {
+		t.Fatalf("New with nested path: %v", err)
+	}
+	for _, sub := range []string{"store", "attachments", "meta"} {
+		if _, err := os.Stat(filepath.Join(dir, sub)); os.IsNotExist(err) {
+			t.Errorf("expected subdirectory %s to be created", sub)
+		}
+	}
+}