feat(mobile): Add mobile-friendly dashboard consumption mode

Adds a mobile-optimized dashboard consumption experience:

- Drawer-based nav and filter menus on mobile
- Full-width chart layout on small screens, with charts stacked
- Compact dashboard header (hidden action buttons that don't apply in
  consumption mode)
- Force card view (and hide the table/card toggle) on the dashboard list
- Full-width cards on the welcome page when viewed on mobile
- Filter drawer for the dashboard list page
- Route guard for pages that don't yet have a mobile experience, with a
  dedicated MobileUnsupported page
- Mock-friendly `Grid.useBreakpoint` plumbing for existing component
  tests, plus a new mobile-focused test suite and Playwright coverage

Squashed from 32 commits on the long-running mobile-dashboard-support
branch and rebased onto current master.

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