D2: JobErrorLine component + home/jobs page integration

- Add src/lib/components/JobErrorLine.svelte: reusable error banner with
  icon, truncated message, accent retry and danger delete buttons; Svelte 5
  runes; WCAG AA (role=alert/status, aria-busy, aria-label, focus ring)
- Integrate into src/routes/+page.svelte: replace .recent-err-line div with
  JobErrorLine; add handleRetry function updating jobs array in-place
- Integrate into src/routes/jobs/+page.svelte: remove inline .job-err-inline
  and .row-retry-slot; add JobErrorLine inside .job-info for failed/cancelled;
  refactor retryJobById/deleteJobById with clean (jobId: string) signatures;
  done-job delete preserved in row-actions
- Add src/tests/job-error-line.test.ts: 8 component rendering tests via
  @testing-library/svelte + happy-dom covering message, buttons, callbacks,
  fallback text, and ARIA roles
- Install @testing-library/svelte@5 and happy-dom as devDeps for component
  test support; update vitest.config.ts with svelte plugin, happy-dom env
  match glob, and browser resolve condition for Svelte 5 client build

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

package.json

@@ -20,9 +20,11 @@
     "@sveltejs/kit": "^2.57.0",
     "@sveltejs/vite-plugin-svelte": "^7.0.0",
     "@tailwindcss/vite": "^4.2.4",
+    "@testing-library/svelte": "^5.4.2",
     "@types/better-sqlite3": "^7.6.13",
     "@types/web-push": "^3.6.4",
     "@vitest/coverage-v8": "^4.1.5",
+    "happy-dom": "^20.10.6",
     "svelte": "^5.55.2",
     "svelte-check": "^4.4.6",
     "typescript": "^6.0.2",