[johnnyhuy]

The showcase search now has a visible label, category buttons expose their selected state, and the result count uses a polite status region. Empty results offer Clear filters, which resets both filters and returns focus to search; the search field also fits narrow screens.

Part of #86. Closes #130 after merge. The parent epic stays open.

Verified with the repository gates and a running local stack.

• mise run install passed with existing peer dependency warnings.
• mise run lint passed across all workspaces, including 51 app files.
• mise run test --runInBand --verbose passed with 45 tests across seven suites; one existing test/suite remains skipped.
• BROWSER=none mise run dev compiled successfully and served the app and backend on 3010/7017 through gitignored local configuration. Another worktree already owns 3000/7007.
• mise run proof-browser run-code passed browser assertions for Space-key category selection, combined filtering, Enter-key reset, all 14 cards returning and focus returning to search. At 375px, the search field stays inside the viewport and reset restores all cards. The temporary local proof-browser task used the installed Playwright CLI with Chrome.
• This is frontend-only. No backend, dependencies or packaging changed, so a Docker image build was not required.

The new behaviour tests passed.

PASS app packages/app/src/components/showcase/ShowcasePage.test.tsx (7.201 s)
  ✓ labels search and exposes the active category and result count (332 ms)
  ✓ combines search and category filters and restores all cards from an empty result (364 ms)
Test Suites: 1 skipped, 7 passed, 7 of 8 total
Tests:       1 skipped, 45 passed, 46 total

Browser capture succeeded on desktop and mobile. No capture method was blocked and no fallback was needed. Screenshots are committed under .tmp/proof/ and linked to this exact commit.

An extra mise run check-types check, using a temporary local task that executes node node_modules/typescript/bin/tsc --incremental false, failed before checking application code. The existing TypeScript ~5.3.0 cannot accept DOM.AsyncIterable from Backstage's compiler defaults (TS6046). The dependency and compiler configuration files match origin/main at 2cdb9eb. Follow-up #131 tracks compiler compatibility and a repository type-check gate; the current lint task runs ESLint only. No manual screen reader session was performed; automated checks verify the accessible names, pressed states, status semantics and keyboard focus behaviour.