feat(datasets): periods (start_date/end_date), dg_id column, date filters; rename observation dates

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/domain/dataset_test.go

@@ -1,6 +1,9 @@
 package domain
 
-import "testing"
+import (
+	"errors"
+	"testing"
+)
 
 func TestFileTypeValid(t *testing.T) {
 	valid := []FileType{FileTypeVectorWithKato, FileTypeVector, FileTypeRaster}
@@ -72,3 +75,31 @@ func TestExtensionAllowedFor(t *testing.T) {
 		}
 	}
 }
+
+func TestValidateDatePeriod(t *testing.T) {
+	s := func(v string) *string { return &v }
+	cases := []struct {
+		name       string
+		start, end *string
+		wantErr    bool
+	}{
+		{"both nil", nil, nil, false},
+		{"start only", s("2020-01-01"), nil, false},
+		{"ordered", s("2020-01-01"), s("2020-12-31"), false},
+		{"same day", s("2020-01-01"), s("2020-01-01"), false},
+		{"reversed", s("2020-12-31"), s("2020-01-01"), true},
+		{"bad start", s("01.01.2020"), nil, true},
+		{"bad end", nil, s("2020-13-01"), true},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := ValidateDatePeriod(tc.start, tc.end)
+			if (err != nil) != tc.wantErr {
+				t.Fatalf("err=%v wantErr=%v", err, tc.wantErr)
+			}
+			if err != nil && !errors.Is(err, ErrValidation) {
+				t.Fatalf("expected ErrValidation, got %v", err)
+			}
+		})
+	}
+}