feat(event): normalize session.status to session.idle

Add session-status-normalizer to handle session.status events and
convert idle status to synthetic session.idle events. Includes
deduplication logic to prevent duplicate idle events within 500ms.

src/plugin/session-status-normalizer.ts

@@ -0,0 +1,22 @@
+type EventInput = { event: { type: string; properties?: Record<string, unknown> } }
+type SessionStatus = { type: string }
+
+export function normalizeSessionStatusToIdle(input: EventInput): EventInput | null {
+	if (input.event.type !== "session.status") return null
+
+	const props = input.event.properties
+	if (!props) return null
+
+	const status = props.status as SessionStatus | undefined
+	if (!status || status.type !== "idle") return null
+
+	const sessionID = props.sessionID as string | undefined
+	if (!sessionID) return null
+
+	return {
+		event: {
+			type: "session.idle",
+			properties: { sessionID },
+		},
+	}
+}