feat: add Yuheng ticket bind, trial SMS off, shared bindings

Ship ticket-exchange and bind/policy for Z13, keep trial binds SMS-free, allow shared company bindings, and align SyncPage plus sync docs.

Co-authored-by: Cursor <cursoragent@cursor.com>

platform/internal/yuhticket/ticket_test.go

@@ -0,0 +1,51 @@
+package yuhticket
+
+import (
+	"testing"
+	"time"
+)
+
+func TestSignVerifyRoundTrip(t *testing.T) {
+	secret := "test-secret"
+	now := time.Unix(1_700_000_000, 0).UTC()
+	c := Claims{
+		Iss: "yuheng", Aud: "aijianzhan", Phone: "13531041944",
+		HostKey: "host-1", Exp: now.Add(90 * time.Second).Unix(), JTI: "jti-ok", Scope: "sync_bind",
+	}
+	tok, err := Sign(secret, c)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, err := Verify(tok, VerifyOpts{Secret: secret, Now: now})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.Phone != c.Phone || got.HostKey != c.HostKey {
+		t.Fatalf("claims mismatch: %+v", got)
+	}
+}
+
+func TestVerifyBadSig(t *testing.T) {
+	now := time.Unix(1_700_000_000, 0).UTC()
+	tok, _ := Sign("a", Claims{
+		Phone: "13800000001", HostKey: "h", Exp: now.Add(60 * time.Second).Unix(), JTI: "j1",
+	})
+	if _, err := Verify(tok, VerifyOpts{Secret: "b", Now: now}); err == nil {
+		t.Fatal("expected bad sig")
+	}
+}
+
+func TestJTIConsume(t *testing.T) {
+	dir := t.TempDir()
+	st, err := NewJTIStore(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	exp := time.Now().Add(time.Minute).Unix()
+	if err := st.Consume("x", exp); err != nil {
+		t.Fatal(err)
+	}
+	if err := st.Consume("x", exp); err == nil {
+		t.Fatal("expected replay")
+	}
+}