feat(frontend): add task loading skeletons

[Dreamstore2046]

Summary

• add frontend skeleton components at the path used by dashboard loading imports
• add a reusable task-list skeleton with accessible busy semantics
• replace the tasks page's generic loading blocks with the task-list skeleton
• remove touched-file \�ny\ casts from the tasks page while wiring the loading state

Closes #698

Validation

• \git diff --check`n-
  px eslint app/tasks/page.tsx components/skeletons/index.tsx --quiet`n

Notes

• Full
  px tsc --noEmit --pretty false --project tsconfig.json\ is blocked by existing baseline parse errors in \components/AIAssistant/hooks/tests/useAIAssistant.test.ts\ where JSX is in a .ts\ file.
• Full
  pm run lint -- --quiet\ is blocked by existing repository-wide lint errors unrelated to this PR.

[Dreamstore2046]

Closing this because the linked Stellar Wave issue #698 already has an accepted contributor through drips-wave, so this PR no longer has a clear reward/settlement path for me. Thanks for the review time.