Publish an IntentSpec JSON sample and round-trip test

Why: the intent library has to publish the shape it owns, without sharing a Go type with the other libraries.
Evidence: GOWORK=off go test -count=1 ./schema/ ./intent/ passed.
Impact: schema/ is new. Recognition behavior is unchanged.
Refs: D1
Co-authored-by: Cursor <cursoragent@cursor.com>

schema/intentspec.sample.json

@@ -0,0 +1 @@
+{"id":"demo.write","domain":"demo","version":1,"matcher":{"includes_any":["写"]}}

schema/roundtrip_test.go

@@ -0,0 +1,34 @@
+package schema
+
+import (
+	"encoding/json"
+	"os"
+	"testing"
+
+	"agent-intent/intent"
+)
+
+func TestIntentSpecRoundTrip(t *testing.T) {
+	raw, err := os.ReadFile("intentspec.sample.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var spec intent.IntentSpec
+	if err := json.Unmarshal(raw, &spec); err != nil {
+		t.Fatal(err)
+	}
+	if spec.ID != "demo.write" || spec.Matcher.IncludesAny[0] != "写" {
+		t.Fatalf("%+v", spec)
+	}
+	back, err := json.Marshal(spec)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var again intent.IntentSpec
+	if err := json.Unmarshal(back, &again); err != nil {
+		t.Fatal(err)
+	}
+	if again.ID != spec.ID || again.Version != 1 {
+		t.Fatalf("%+v", again)
+	}
+}