feat: derive dashboard outline from visible sections

[ItsThompson]

Summary

• derive dashboard outline links from visible dashboard DOM sections
• add root-scoped mutation and intersection observer behavior
• add tests for ordering, nesting, visibility, mutations, conditional sections, and active styling

Verification

• npm run test -- DashboardOutline
• npm run test
• npx tsc --noEmit
• npm run lint

Note: npm run build completed Vite output but emitted existing Module Federation DTS TYPE-001 warning for src/features/settings/hooks/useDefaultBudget.ts.