feat(core-shared): add rate-limit type primitives and manifest field

Adds IRateLimit, RateLimitBudget, RateLimitDecision to a new
rate-limit sub-module; adds RateLimited<F> brand and isRateLimited
predicate following the Captured/ConsentChecked pattern; extends
UseCaseManifest with rateLimit?: readonly RateLimitBudget[] so
features can declare rate-limit gates in their manifests.

Exports new types from @repo/core-shared/rate-limit and
@repo/core-shared/conformance. Blocks stories 02, 03, and 04.

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

packages/core-shared/src/conformance/index.ts

@@ -3,6 +3,7 @@ export type {
   Captured,
   Analyzed,
   ConsentChecked,
+  RateLimited,
 } from "./brands";
 export type { FeatureManifest, UseCaseManifest } from "./define-feature";
 export { defineFeature } from "./define-feature";
@@ -29,6 +30,7 @@ export {
   isAudited,
   isAnalyzed,
   isConsentChecked,
+  isRateLimited,
 } from "./brand-runtime";
 export { ConformanceError } from "./conformance-error";
 export { assertFeatureConformance } from "./assert-bindings";