feat(frontend): make Storybook a validated, fully covered component workbench

Storybook existed only as an undocumented local tool: 9 of 24 reusable components had stories, autodocs pages were bare prop tables, nothing built or tested the stories, and no contributor doc mentioned the workbench existed.

Every reusable component under src/components/ now has a co-located story with enriched autodocs (component descriptions plus per-prop argTypes, kept as string metadata since the repo bans line comments). Stories double as headless Chromium tests through the Storybook vitest addon, with axe accessibility checks enforced as errors and play-function interaction tests covering the modals, the RHF field bridge, the config block, and the select-all buttons. The preview now mirrors the panel's real theme DOM (body class, shared AntD theme config, seeded theme storage) so what stories render matches production.

CI and make verify gain a static Storybook build as a compile gate, and the frontend test job installs Chromium so story tests run on every PR. Contributor docs (frontend README, CONTRIBUTING, agent guides) document the workbench, the story conventions, and the Controls setup. Node engines move to 24 LTS and gen:api drops the type-stripping flags that Node 24 makes default.

.github/workflows/ci.yml

@@ -168,12 +168,18 @@ jobs:
       - name: Typecheck
         run: npm run typecheck
         working-directory: frontend
+      - name: Install Playwright Chromium (Storybook story tests)
+        run: npx playwright install --with-deps chromium
+        working-directory: frontend
       - name: Test
         run: npm test
         working-directory: frontend
       - name: Build
         run: npm run build
         working-directory: frontend
+      - name: Build Storybook
+        run: npm run build-storybook
+        working-directory: frontend
       - name: Audit
         run: npm audit --audit-level=high
         working-directory: frontend