feat(dashboard): creative UX overhaul with storytelling and visual depth

[rajnavakoti]

Summary

• Hero section with animated stat counters, compelling tagline, and estimated total pipeline value
• Color-coded pipeline stages with connector arrows and per-status accent colors
• Pie chart (pure CSS conic-gradient) for category breakdown with legend
• Progress ring gauges for graduation rate, selection rate, average score, and decisions made
• Expandable submission cards — click to reveal problem statement, value estimate, effort, tech stack, and demo/issue links
• Softer dark mode — swapped pure black (#111) for dark slate (#1a1a2e) with layered surfaces
• Better hover effects — subtle scale + lift instead of jarring color inversion
• Enriched data — submissions.json now includes problem, value, effort, techStack, demoUrl fields
• Still zero frameworks, zero build steps, fully accessible

Issues Closed

Closes #36, Closes #37, Closes #38

Test plan

• Hero counters animate on load
• Pipeline shows all 8 stages with correct color-coded top borders
• Pie chart renders proportionally with correct category colors
• Progress ring gauges animate in smoothly
• Clicking a card expands to show detail section
• Clicking again (or pressing Enter/Space) collapses it
• Dark mode is visibly softer than before (not pure black)
• Table/card hover uses subtle highlight, not color inversion
• Responsive at 320px, 768px, 1024px, 1440px
• Links inside cards still work without triggering expand

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