feat(core-analytics): add IAnalytics interface, types, and NoopAnalytics

Replaces generator placeholder with IAnalytics interface (track, identify,
pageView, flush), AnalyticsAttributeValue + AnalyticsUser types, and
NoopAnalytics implementation. Adds sibling tests covering all four methods
with 100% coverage. All conformance + coverage gates pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core-analytics/src/analytics.interface.ts

@@ -0,0 +1,21 @@
+export type AnalyticsAttributeValue = string | number | boolean;
+
+export type AnalyticsUser = {
+  id: string;
+};
+
+export interface IAnalytics {
+  track(
+    event: string,
+    attributes?: Record<string, AnalyticsAttributeValue>,
+  ): void;
+  identify(
+    user: AnalyticsUser,
+    attributes?: Record<string, AnalyticsAttributeValue>,
+  ): void;
+  pageView(
+    path: string,
+    attributes?: Record<string, AnalyticsAttributeValue>,
+  ): void;
+  flush(): Promise<void>;
+}