feat(core-shared): add NoopRateLimit and InMemoryRateLimit implementations

NoopRateLimit always allows with Infinity remaining — zero-overhead default
for apps without a wired rate-limit impl. InMemoryRateLimit uses a Map-backed
fixed-window with check-at-read expiry and an injected clock for testability.
Both exported from the core-shared barrel.

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

packages/core-shared/src/rate-limit/noop-rate-limit.ts

@@ -0,0 +1,15 @@
+import type { IRateLimit, RateLimitDecision } from "./rate-limit.interface";
+
+const EPOCH = new Date(0);
+
+export class NoopRateLimit implements IRateLimit {
+  async consume(
+    _budgetName: string,
+    _key: string,
+    _weight?: number,
+  ): Promise<RateLimitDecision> {
+    return { allowed: true, remaining: Infinity, resetAt: EPOCH };
+  }
+
+  async reset(_budgetName: string, _key: string): Promise<void> {}
+}