Simplify student and mentor workflows

[eeminionn]

Summary

• make each assigned task row directly actionable and reduce the student dashboard to one primary next step
• replace compiler jargon with clear results and next-step language for beginners
• remove duplicate mentor navigation and prioritize review work, overdue tasks, daily activity and class size
• derive the review badge and queue from the same available submissions
• turn review criteria into an optional plain-language checklist and guard missing mission versions
• document the heuristic review and defer large unvalidated features

Interaction review

The audit applies public human-centered design and usability guidance from Stanford d.school, MIT and UDD. It does not claim institutional endorsement. See docs/UX_AUDIT_AULA_3_3.md.

Validation

• pnpm check
• pnpm check:frontend
• pnpm exec playwright test --config v2/playwright.config.ts --workers=1 (24 passed, 4 sandbox tests skipped)
• pnpm test:e2e:frontend -- --workers=1 (4 passed)
• Judge0 live smoke test: JavaScript, Python and C++ returned Accepted
• desktop visual inspection and mobile overflow tests

Scope

Issues #56 and #59 remain open intentionally because they track assignment notifications.

Closes #68

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