Summary

Add tests in apps/web to verify profile page renders profile data and handles missing users.

Tasks

• use @testing-library/svelte to create apps/web/src/routes/u/[username]/+page.test.ts.
• mock the loader data to include a profile and assert name/avatar rendered.
• mock loader error to assert 'User Not Found' message appears.

Acceptance Criteria

• tests can run with pnpm --filter @devcard/web test (or app-specific command).
• this makes web path robust for newcomers.