feat(presentation): build third progress presentation deck

[hwangjokim]

Summary

• add a dedicated third presentation page and route
• replace the third deck middle slides with progress-plan, timeline, status, and stack content
• refine timeline markers, page numbers, and backend/frontend stack separation

Validation

• pnpm tsc --noEmit ✅
• pnpm biome lint . ✅
• pnpm build ✅ (Vite warned that Node 20.15.0 is below the recommended 20.19+)

Closes #15

[vercel]

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Project	Deployment	Actions	Updated (UTC)
client	Ready	Preview, Comment	Mar 21, 2026 5:38pm