feat: ship loose-offline dbsync (validate, agent push, LWW audit)

Add UUID/FK channel checks, agent whitelist/push APIs, bindings, super-admin LWW audit with rollback, reconcile rate limits, and sync docs. Default customers stay opt-in; company conflict UI is removed.

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

platform/internal/dbsync/binding_test.go

@@ -0,0 +1,35 @@
+package dbsync
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+func TestEnsureBindingUpsert(t *testing.T) {
+	dir := t.TempDir()
+	st, err := NewFileStore(filepath.Join(dir, "dbsync"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	b, err := st.EnsureBinding(Binding{
+		TenantID:        1,
+		LocalDatabaseID: "local-a",
+		OnlineDBID:      "online-1",
+		ChannelID:       "ch1",
+	})
+	if err != nil || b.ID == "" {
+		t.Fatalf("ensure: %+v err=%v", b, err)
+	}
+	b2, err := st.EnsureBinding(Binding{
+		TenantID:        1,
+		LocalDatabaseID: "local-a",
+		OnlineDBID:      "online-2",
+	})
+	if err != nil || b2.OnlineDBID != "online-2" || b2.ID != b.ID {
+		t.Fatalf("upsert: %+v err=%v", b2, err)
+	}
+	list, err := st.ListBindings(1, "local-a")
+	if err != nil || len(list) != 1 {
+		t.Fatalf("list=%d err=%v", len(list), err)
+	}
+}