Add skip-to-content links on dashboard, demo, and status

## Task

Static operator pages have some aria labels but no skip-to-main link for keyboard users.

## Files

- `dashboard/index.html` + CSS
- `public/demo/index.html` + CSS
- `public/status/index.html` + CSS

## Acceptance criteria

- [ ] First focusable control is a skip link targeting ``
- [ ] Visible on focus, hidden otherwise
- [ ] No landing-hero layout shift (landing optional)
- [ ] Optional Playwright tab-focus assertion

Inspect dashboard/index.html, public/demo/index.html, public/status/index.html, and their associated CSS first. Verify the current focus order and styling, then check any existing Playwright setup for the optional tab-focus assertion. Done means each page starts keyboard focus on a skip link targeting , the link appears only on focus, and the landing layout does not shift.

Written by the indexing model from the issue text.