docs(adr): ADR-011 TDD foundation; update AGENTS.md per-feature

Captures the decision to add @repo/core-testing, factories, contract
suites, vitest safety defaults, coverage thresholds, Storybook
test-runner, and CI as one cohesive TDD foundation. Per-feature
AGENTS.md gains a Tests section pointing to factories, contract suite,
and the canonical test commands.

Spec: §7.4, §7.5

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

AGENTS.md

@@ -20,6 +20,7 @@ This is a **Turborepo + pnpm monorepo** organized by vertical features. Each fea
 | `@repo/navigation` | feature | Header global |
 | `@repo/core-eslint` | tooling | Shared ESLint 9 flat configs (base, next, react-internal, boundaries) |
 | `@repo/core-typescript` | tooling | Shared TypeScript base configs + Vitest base |
+| `@repo/core-testing` | tooling | Shared test utilities (defineFactory, defineContractSuite, renderWithProviders, payload mocks) |
 
 ---
 
@@ -31,7 +32,7 @@ This is a **Turborepo + pnpm monorepo** organized by vertical features. Each fea
 - **core-composition** (3 packages) — `packages/core-api`, `core-cms`, `core-trpc`
 - **core** (2 packages) — `packages/core-shared`, `core-ui`
 - **feature** (5 packages) — `packages/auth`, `blog`, `media`, `marketing-pages`, `navigation`
-- **tooling** (2 packages) — `packages/core-eslint`, `core-typescript`
+- **tooling** (3 packages) — `packages/core-eslint`, `core-typescript`, `core-testing`
 
 ### Allowed dependency directions
 
@@ -212,5 +213,5 @@ Per-package documentation lives in each `AGENTS.md`:
 - `packages/core-api/AGENTS.md`, `core-cms/AGENTS.md`, `core-trpc/AGENTS.md`
 - `packages/core-ui/AGENTS.md`
 - `packages/auth/AGENTS.md`, `blog/AGENTS.md`, `media/AGENTS.md`, `marketing-pages/AGENTS.md`, `navigation/AGENTS.md`
-- `packages/core-eslint/AGENTS.md`, `core-typescript/AGENTS.md`
+- `packages/core-eslint/AGENTS.md`, `core-typescript/AGENTS.md`, `core-testing/AGENTS.md`
 - `apps/cms/AGENTS.md`, `web-next/AGENTS.md`, `web-tanstack/AGENTS.md`, `storybook/AGENTS.md`