Add retry mechanism and failure notifications for nCore/qBittorrent setup

- Implemented a retry mechanism for external calls, allowing up to 3 attempts before failing.
- Enhanced error handling to send failure notifications when setup steps fail, including detailed error messages.
- Updated RunSummary model to include status, error step, and error message fields for better tracking of run outcomes.
- Modified database schema to store failure metadata for runs.
- Updated README.md to reflect changes in error handling and notification behavior.

internal/store/store_test.go

@@ -43,3 +43,42 @@ func TestMarkResolvedResolvesManualNeededTorrent(t *testing.T) {
 		t.Fatalf("expected last_resolved_at %q, got %q", resolvedAt.Format(time.RFC3339), got.LastResolvedAt)
 	}
 }
+
+func TestInsertRunRecordsFailureMetadata(t *testing.T) {
+	db, err := Open(t.TempDir() + "/state.sqlite")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+
+	startedAt := time.Date(2026, 5, 7, 11, 0, 0, 0, time.UTC)
+	if err := db.InsertRun(model.RunSummary{
+		StartedAt:    startedAt,
+		Status:       "failed",
+		ErrorStep:    "fetch nCore HnR page",
+		ErrorMessage: "timeout",
+		DryRun:       true,
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	stats, err := db.Stats()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if stats.LastRun == nil {
+		t.Fatal("expected last run")
+	}
+	if stats.LastRun.Status != "failed" {
+		t.Fatalf("expected status failed, got %q", stats.LastRun.Status)
+	}
+	if stats.LastRun.ErrorStep != "fetch nCore HnR page" {
+		t.Fatalf("expected error step to be recorded, got %q", stats.LastRun.ErrorStep)
+	}
+	if stats.LastRun.ErrorMessage != "timeout" {
+		t.Fatalf("expected error message to be recorded, got %q", stats.LastRun.ErrorMessage)
+	}
+	if !stats.LastRun.DryRun {
+		t.Fatal("expected dry-run to be recorded")
+	}
+}