Fix area calculations and shapefile export in geometry tutorial

## Issues Fixed

### 1. Incorrect population density calculations
- **Bug**: Area calculated in geographic CRS (degrees²) instead of projected CRS (m²)
- **Result**: Nonsensical densities like 46 trillion people/km²
- **Fix**: Reproject to EPSG:3347 before calculating areas
- **Impact**: Now shows correct densities (Vancouver: 5,745 people/km²)

### 2. Shapefile export warnings
- **Issue**: Column names > 10 chars truncated by shapefile format
- **Issue**: Computed pop_density values too large for shapefile field width
- **Fix**:
  - Export only base columns (geometry, name, v_CA21_1, v_CA21_434)
  - Rename to shapefile-friendly names (pop2021, income)
  - Changed from .to_excel() to .to_csv() for WKT export

### 3. Redundant CRS section
- Removed duplicate CRS conversion code
- Simplified to show CRS info and conversion examples
- Added common Canadian CRS reference list

## Build Results
- All geographic calculations now correct ✅
- No shapefile warnings about field width ✅
- Tutorial flow improved ✅

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: dshkol