Remove overengineered components, add Streamlit web UI

- Remove 110+ files of non-essential components:
  - benchmarks/ directory (performance testing infrastructure)
  - socialmapper/security/ (enterprise key management)
  - socialmapper/export/ (multi-format export system)
  - socialmapper/visualization/ (choropleth module)
  - socialmapper/performance/batch.py, memory.py
  - docs/archive/, docs/tutorials/ (outdated documentation)
  - examples/tutorials/ (tutorial scripts)
  - scripts/ (deployment, monitoring, community automation)
  - .github/ community infrastructure files
  - Strategic planning documents

- Add Streamlit web interface for no-code usage:
  - socialmapper/app.py: Interactive web app with map visualization
  - socialmapper/cli.py: CLI launcher for the web app
  - Supports isochrone, POI discovery, and census analysis
  - Export functionality for GeoJSON and CSV

- Fix imports after module removal:
  - _census.py: Use os.environ for API key
  - distance/engine.py: Fix validator import
  - isochrone/clustering.py: Fix validator import
  - performance/__init__.py: Remove deleted module imports

- Update pyproject.toml with streamlit dependencies
- Update README.md to promote web UI

This reduces complexity while maintaining all 5 core API functions.

Author: mihiarc