docs: add industry research and update PRD v0.2 with competitive analysis
- Add INDUSTRY_RESEARCH.md: market sizing, 9 competitors, 24 feature demands, trends
- Update PRD to v0.2: Next.js 16 + React 19 + TailwindCSS v4 stack
- Add visual timeline, Pomodoro, neurodivergent mode, AI reschedule features
- Promote iOS + Apple Watch to v1.0, add new v1.1 context phase
- Expand competitive analysis (Tiimo, Structured, Alarmy, TickTick, Forest, etc.)
- Add risk assessment section, revised monetization (Family tier)
- Update development phases to realistic 11-week roadmap
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