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/rules/loader.go

@@ -39,6 +39,9 @@ func Load(fsys fs.FS) ([]Rule, error) {
 		if r.Version == 0 {
 			return nil, fmt.Errorf("rules: %s: missing version", entry.Name())
 		}
+		if r.Jurisdiction == "" {
+			return nil, fmt.Errorf("rules: %s: missing land (jurisdiction)", entry.Name())
+		}
 		if seen[r.ID] {
 			return nil, fmt.Errorf("rules: %s: duplicate rule id %s", entry.Name(), r.ID)
 		}