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/define-feature.test.ts

@@ -2,7 +2,9 @@ import { describe, it, expect, expectTypeOf } from "vitest";
 import {
   defineFeature,
   type FeatureManifest,
+  type UseCaseManifest,
 } from "@/conformance/define-feature";
+import type { RateLimitBudget } from "@/rate-limit/rate-limit.interface";
 import {
   DEFAULT_COVERAGE_BANDS,
   DEFAULT_MUTATION_SCORE,
@@ -58,6 +60,41 @@ describe("defineFeature", () => {
     expectTypeOf(manifest).toMatchTypeOf<FeatureManifest>();
   });
 
+  it("accepts an optional rateLimit array on a use case", () => {
+    const manifest = defineFeature({
+      name: "auth",
+      requiredCores: [],
+      useCases: {
+        signIn: {
+          mutates: false,
+          audits: [],
+          publishes: [],
+          consumes: [],
+          rateLimit: [{ name: "login", window: "1m", budget: 5 }],
+        },
+      },
+      realtimeChannels: [],
+      jobs: [],
+    } as const);
+
+    expectTypeOf(manifest).toMatchTypeOf<FeatureManifest>();
+    expectTypeOf(manifest.useCases.signIn.rateLimit).toMatchTypeOf<
+      readonly RateLimitBudget[] | undefined
+    >();
+  });
+
+  it("use case without rateLimit satisfies UseCaseManifest", () => {
+    const uc: UseCaseManifest = {
+      mutates: false,
+      audits: [],
+      publishes: [],
+      consumes: [],
+    };
+    expectTypeOf(uc.rateLimit).toEqualTypeOf<
+      readonly RateLimitBudget[] | undefined
+    >();
+  });
+
   it("accepts an optional coverage section", () => {
     const manifest = defineFeature({
       name: "auth",