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/index/index_test.go

@@ -0,0 +1,192 @@
+package index_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/archivmail/internal/index"
+)
+
+// newXapianIndex creates a temporary Xapian index for testing.
+func newXapianIndex(t *testing.T) index.Indexer {
+	t.Helper()
+	idx, err := index.New(t.TempDir(), 100, "xapian")
+	if err != nil {
+		t.Skip("xapian not available:", err)
+	}
+	t.Cleanup(func() { idx.Close() })
+	return idx
+}
+
+func seedDocs(t *testing.T, idx index.Indexer) {
+	t.Helper()
+	docs := []index.MailDocument{
+		{
+			ID:      "aaa111",
+			From:    "alice@example.com",
+			To:      "bob@example.com",
+			Subject: "Invoice Q1-2026",
+			Body:    "Please find attached the invoice for January.",
+			Date:    time.Date(2026, 1, 15, 10, 0, 0, 0, time.UTC),
+			Size:    1024,
+		},
+		{
+			ID:      "bbb222",
+			From:    "bob@example.com",
+			To:      "alice@example.com charlie@example.com",
+			Subject: "Meeting Agenda",
+			Body:    "Agenda for the quarterly review meeting.",
+			Date:    time.Date(2026, 2, 1, 9, 0, 0, 0, time.UTC),
+			Size:    512,
+		},
+		{
+			ID:            "ccc333",
+			From:          "charlie@example.com",
+			To:            "alice@example.com",
+			Subject:       "Offer with attachment",
+			Body:          "Please review the attached offer document.",
+			AttachNames:   "offer.pdf",
+			HasAttachment: true,
+			Date:          time.Date(2026, 3, 1, 14, 0, 0, 0, time.UTC),
+			Size:          8192,
+		},
+	}
+	for _, d := range docs {
+		if err := idx.IndexSync(d); err != nil {
+			t.Fatalf("IndexSync %s: %v", d.ID, err)
+		}
+	}
+}
+
+func TestIndexAndSearchFulltext(t *testing.T) {
+	idx := newXapianIndex(t)
+	seedDocs(t, idx)
+
+	result, err := idx.Search(index.SearchRequest{Query: "invoice", PageSize: 10})
+	if err != nil {
+		t.Fatalf("Search: %v", err)
+	}
+	if result.Total == 0 {
+		t.Error("expected at least 1 hit for 'invoice'")
+	}
+	if result.Hits[0].ID != "aaa111" {
+		t.Errorf("top hit = %q, want aaa111", result.Hits[0].ID)
+	}
+}
+
+func TestSearchMatchAll(t *testing.T) {
+	idx := newXapianIndex(t)
+	seedDocs(t, idx)
+
+	result, err := idx.Search(index.SearchRequest{PageSize: 25})
+	if err != nil {
+		t.Fatalf("Search all: %v", err)
+	}
+	if result.Total != 3 {
+		t.Errorf("expected 3 total hits, got %d", result.Total)
+	}
+}
+
+func TestSearchFromFilter(t *testing.T) {
+	idx := newXapianIndex(t)
+	seedDocs(t, idx)
+
+	result, err := idx.Search(index.SearchRequest{
+		From:     "alice@example.com",
+		PageSize: 25,
+	})
+	if err != nil {
+		t.Fatalf("Search from: %v", err)
+	}
+	if result.Total != 1 {
+		t.Errorf("expected 1 hit from alice, got %d", result.Total)
+	}
+}
+
+func TestSearchDateRange(t *testing.T) {
+	idx := newXapianIndex(t)
+	seedDocs(t, idx)
+
+	from := time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC)
+	to := time.Date(2026, 2, 1, 23, 59, 59, 0, time.UTC)
+	result, err := idx.Search(index.SearchRequest{
+		DateFrom: &from,
+		DateTo:   &to,
+		PageSize: 25,
+	})
+	if err != nil {
+		t.Fatalf("Search date range: %v", err)
+	}
+	if result.Total != 2 {
+		t.Errorf("expected 2 hits in Jan-Feb 2026, got %d", result.Total)
+	}
+}
+
+func TestSearchOwnEmail(t *testing.T) {
+	idx := newXapianIndex(t)
+	seedDocs(t, idx)
+
+	// charlie@example.com sent 1 mail and received 1 mail = should see 2
+	result, err := idx.Search(index.SearchRequest{
+		OwnEmail: "charlie@example.com",
+		PageSize: 25,
+	})
+	if err != nil {
+		t.Fatalf("Search OwnEmail: %v", err)
+	}
+	if result.Total < 1 {
+		t.Errorf("charlie should see at least 1 mail, got %d", result.Total)
+	}
+}
+
+func TestSearchPagination(t *testing.T) {
+	idx := newXapianIndex(t)
+	seedDocs(t, idx)
+
+	page0, _ := idx.Search(index.SearchRequest{PageSize: 2, Page: 0})
+	page1, _ := idx.Search(index.SearchRequest{PageSize: 2, Page: 1})
+
+	if len(page0.Hits) != 2 {
+		t.Errorf("page 0: expected 2 hits, got %d", len(page0.Hits))
+	}
+	if len(page1.Hits) != 1 {
+		t.Errorf("page 1: expected 1 hit, got %d", len(page1.Hits))
+	}
+	// No overlap
+	if page0.Hits[0].ID == page1.Hits[0].ID {
+		t.Error("pagination returned duplicate results")
+	}
+}
+
+func TestDelete(t *testing.T) {
+	idx := newXapianIndex(t)
+	seedDocs(t, idx)
+
+	if err := idx.Delete("aaa111"); err != nil {
+		t.Fatalf("Delete: %v", err)
+	}
+
+	result, _ := idx.Search(index.SearchRequest{Query: "invoice", PageSize: 10})
+	for _, h := range result.Hits {
+		if h.ID == "aaa111" {
+			t.Error("deleted document still in results")
+		}
+	}
+}
+
+func TestUnknownBackend(t *testing.T) {
+	_, err := index.New(t.TempDir(), 10, "elasticsearch")
+	if err == nil {
+		t.Error("expected error for unknown backend")
+	}
+}
+
+func TestXapianNotCompiledError(t *testing.T) {
+	_, err := index.New(t.TempDir(), 10, "xapian")
+	// Without -tags xapian this must return a helpful error
+	if err == nil {
+		t.Log("xapian compiled in — skipping stub error test")
+	} else {
+		t.Logf("xapian stub error (expected): %v", err)
+	}
+}