fix(go/fio): accept 2-digit year format in transparent date parser

Fio's transparent account page now serves dates as DD.MM.YY (e.g.
07.05.26) rather than the previously expected 4-digit-year format.
Extends parseCzechDate to try all eight layout variants: padded and
non-padded, dot and slash separators, 4-digit and 2-digit years.

Go maps 2-digit year 00-68 → 2000-2068, so 26 → 2026.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

go/internal/io/fio/fio_test.go

@@ -97,6 +97,9 @@ func TestParseCzechDate(t *testing.T) {
 		{"10/04/2026", "2026-04-10"},
 		{"7.5.2026", "2026-05-07"},  // non-padded — real Fio transparent page format
 		{"3.12.2025", "2025-12-03"}, // non-padded single-digit day, double-digit month
+		{"07.05.26", "2026-05-07"},  // padded 2-digit year — current Fio transparent page format
+		{"7.5.26", "2026-05-07"},   // non-padded 2-digit year
+		{"07/05/26", "2026-05-07"}, // slash variant
 		{"", ""},
 		{"invalid", ""},
 	}