Add harness workflow and Material showcase design system

docs/exec-plans/2026-03-23-harness-rollout.md

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+# Harness Rollout Completion
+
+- Status: `completed`
+- Owner: `codex`
+- Date: `2026-03-23`
+
+## Goal
+
+Finish the next harness-engineering layer for Cadence UI by stabilizing baseline validation,
+adding diff-aware suite selection, and exposing worktree-oriented orchestration defaults.
+
+## Scope
+
+- In scope:
+  - fix the current lint failures
+  - stabilize the flaky Storybook smoke route
+  - add suite selection from git diff and working tree changes
+  - add orchestration wrapper docs and scripts
+- Out of scope:
+  - automated plan-to-task decomposition
+  - CI artifact uploads for harness JSON reports
+  - stronger container or VM isolation around worker execution
+
+## Constraints
+
+- Keep the existing validation commands working as direct entrypoints.
+- Do not make the repository depend on a single hosted orchestration service.
+- Preserve simple local development workflows alongside the richer harness path.
+
+## Affected Surfaces
+
+- `apps/docs/src/components/*`
+- `packages/ui/src/components/*`
+- `tests/e2e/storybook-smoke.spec.ts`
+- `scripts/harness/*`
+- `.github/workflows/harness-validate.yml`
+- `docs/harness-engineering.md`
+- `docs/orchestration.md`
+
+## Plan
+
+1. Repair the failing lint issues in stories, tests, and hooks-heavy components.
+2. Stabilize Storybook smoke navigation so it waits for iframe story readiness.
+3. Add a shared diff-to-suite selector and a changed-suite validator.
+4. Expose a repository-local orchestration wrapper with strict worktree defaults.
+5. Update docs and workflow wiring around the new control plane.
+
+## Validation
+
+- `pnpm lint`
+- `pnpm harness:suites`
+- `pnpm harness:select -- --json`
+- `pnpm harness:validate:changed -- --dry-run`
+- `pnpm test`
+- `pnpm typecheck`
+- `pnpm build:docs`
+- `pnpm test:e2e:smoke`
+
+## Orchestration Task Sketch
+
+- `T1`: stabilize validation surfaces
+- `T2`: add selector and reporting control plane
+- `T3`: wire worktree dispatch defaults and docs
+- `T4`: validate changed-suite and full smoke behavior
+
+## Status Log
+
+- `2026-03-23 12:36` fixed existing lint errors in stories, tests, and component hooks
+- `2026-03-23 12:43` stabilized Storybook smoke route readiness via story-title waits
+- `2026-03-23 12:50` added shared harness core, diff-aware suite selector, and changed-suite execution
+- `2026-03-23 12:55` added orchestration wrapper and repository docs for worktree-backed dispatch