refactor: deduplicate numericOnly and DuckDuckGo result extraction

- Extract identical numericOnly inline functions from powerball and
  megamillions into shared sites/internal/parse.NumericOnly with tests
- Extract duplicated DuckDuckGo result parsing from Search() and
  GetResults() into shared extractResults() helper

Closes #13, #14

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

sites/internal/parse/parse_test.go

@@ -0,0 +1,25 @@
+package parse
+
+import "testing"
+
+func TestNumericOnly(t *testing.T) {
+	tests := []struct {
+		input string
+		want  float64
+	}{
+		{"$1.5 Billion", 1.5},
+		{"$100 Million", 100},
+		{"$200,000", 200000},
+		{"no numbers", 0},
+		{"", 0},
+		{"42", 42},
+		{"3.14159", 3.14159},
+	}
+
+	for _, tt := range tests {
+		got := NumericOnly(tt.input)
+		if got != tt.want {
+			t.Errorf("NumericOnly(%q) = %v, want %v", tt.input, got, tt.want)
+		}
+	}
+}