docs(readme): full rewrite reflecting Theis-based redesign

- New demo screenshot (docs/screenshots/demo.png) showing real interference gradient,
  depression cones with isolines, time slider, and structured chat output card
- Replaced cosmetic feature descriptions with what the visuals actually represent
  (Theis coefficients, donor/victim relationships, scipy contour-based isolines)
- Updated Tech Stack: 7 MCP tools, agentic loop, scikit-image, Recharts
- Added project structure for new components (Interference/DrawdownCardView,
  TimeSlider, ConeModeToggle, DrawdownLegend, InterferencePopup)
- API table now lists /api/tools/{analyze_interference,compute_drawdown_grid}
  and /api/metrics/run/{,status} endpoints
- Test count 117 → 154; bumped badge
- Roadmap section: A0 (line UX), A1 (regional grid), LLM diversity

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: CreatmanCEO