Fix frontend lint warnings (CSS, ARIA, Svelte reactivity)

[oldsj]

Summary

Several lint warnings in the frontend that should be cleaned up:

CSS @import positioning

• File: frontend/src/app.css:5
• Issue: @import for Google Fonts should precede all other statements

Svelte a11y warnings

• File: frontend/src/lib/components/TasksPanel.svelte:793

• Issue: <div> with click/keydown handler needs an ARIA role

• File: frontend/src/lib/components/MobileTabBar.svelte:28,53

• Issue: aria-selected not supported by implicit button role - should use role="tab" or remove attribute

Svelte reactivity warning

• File: frontend/src/lib/components/LogViewer.svelte:11
• Issue: logsContainer is updated but not declared with $state() - should be fine for DOM refs but worth reviewing

Origin

These are preexisting issues surfaced during DevSpace dev environment startup.