feat: add jurisdiction field to rules, facts and extraction

Rule now carries a required Jurisdiction (land) field, and Facts a
matching Jurisdiction supplied by the caller (like Platform — no
legal jurisdiction can be read off a caption or image, so the model
never guesses it). Evaluate() only lets a rule fire when its
jurisdiction matches the facts' jurisdiction.

This is the structural half of "deutsche Rechtslage zuerst, Struktur
für Österreich und Schweiz vorgesehen": a future AT/CH rule set can be
added as plain new YAML files without touching existing DE rules, but
no AT/CH content is added now — that needs its own legal research
first, same as WK-001/WK-004 needed for Germany.

WK-001 and WK-004 are tagged land: DE, all golden fixtures carry
jurisdiction: DE, and extract.Input passes Jurisdiction through
unchanged into the returned Facts.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/extract/client_test.go

@@ -86,6 +86,7 @@ func TestExtractSuccess(t *testing.T) {
 
 	got, err := c.Extract(context.Background(), extract.Input{
 		Platform:       "instagram",
+		Jurisdiction:   "DE",
 		Caption:        "Schaut euch dieses Produkt an! Werbung wegen ...",
 		ImageMediaType: "image/jpeg",
 		ImageData:      []byte("fake-jpeg-bytes"),
@@ -96,6 +97,7 @@ func TestExtractSuccess(t *testing.T) {
 
 	want := rules.Facts{
 		Platform:            "instagram",
+		Jurisdiction:        "DE",
 		Consideration:       rules.ConsiderationPaid,
 		DisclosurePresent:   true,
 		DisclosureWording:   "Werbung",