Add Workbench accessibility baseline

[smithaldon1]

Summary

• Add a skip link and named main content target to the Operations Workbench shell.
• Strengthen visible focus states for navigation, links, buttons, inputs, and textareas.
• Add recommendation decision form helper/status text so disabled, available, and submitting states are communicated.
• Clarify evidence timeline semantics with an ordered timeline label and screen-reader-only item ordering text.
• Add static accessibility/contrast assertions and extend Playwright smoke coverage for keyboard interaction.

Closes #179

Test Evidence

• cd apps/web && npm test: 14 passed
• cd apps/web && npm run lint: passed
• cd apps/web && npm run typecheck: passed
• git diff --check: passed
• make test-e2e: initially failed because prior local API/Next servers were still using ports 8000 and 3000; stopped those local processes and reran successfully: 1 passed
• make lint: passed
• make typecheck: passed
• make docs: passed (Markdown-only docs checker placeholder)
• make test: 195 passed
• cd apps/web && npm run build: passed

Docs Impact

• Updated docs/demo/OPERATIONS_WORKBENCH_DEMO_RUNBOOK.md with the keyboard/semantic accessibility rehearsal checklist and remaining non-blocking accessibility debt.
• Updated docs/LEARNING_LOG.md with the issue UX: Add accessibility baseline for demo UI #179 learning summary.

Follow-up Work

• No follow-up required for this issue. Full WCAG certification, a full automated accessibility suite, visual regression testing, and mobile-first redesign remain out of scope.

[smithaldon1]

Reviewed and approved for merge