feat(examples): add sample-app spec

Introduce examples/sample-app/spec.ts — a minimal property-based spec that
taps the sample app's "Click me" button and asserts click_count is
monotonic. Bundle-check and the trace writer test now reference the new
path.

internal/trace/writer_test.go

@@ -20,7 +20,7 @@ func TestWriteMeta_RoundTrip(t *testing.T) {
 
 	meta := Meta{
 		Seed:         42,
-		SpecPath:     "examples/specs/merchant-ledger.ts",
+		SpecPath:     "examples/sample-app/spec.ts",
 		BundleSHA256: "deadbeef",
 		Platform:     "android",
 		BundleID:     "in.okcredit.merchant",