Add comprehensive validation system and migrate to .env configuration

This commit includes:

1. Database Configuration Migration:
   - Migrated from DB.txt (Java JDBC) to .env (python-dotenv)
   - Added .env.example template with clear variable names
   - Updated database.py to use environment variables
   - Added python-dotenv>=1.0.0 to dependencies
   - Updated .gitignore to exclude sensitive files

2. Validation System (1,294 lines):
   - comparator.py: Statistical comparison with RMSE, correlation, tolerances
   - db_extractor.py: Database queries for all sensor types
   - validator.py: High-level validation orchestration
   - cli.py: Command-line interface for validation
   - README.md: Comprehensive validation documentation

3. Validation Features:
   - Compare Python vs MATLAB outputs from database
   - Support for all sensor types (RSN, Tilt, ATD)
   - Statistical metrics: max abs/rel diff, RMSE, correlation
   - Configurable tolerances (abs, rel, max)
   - Detailed validation reports
   - CLI and programmatic APIs

4. Examples and Documentation:
   - validate_example.sh: Bash script example
   - validate_example.py: Python programmatic example
   - Updated main README with validation section
   - Added validation workflow and troubleshooting guide

Benefits:
- ✅ No Java driver needed (native Python connectors)
- ✅ Secure .env configuration (excluded from git)
- ✅ Comprehensive validation against MATLAB
- ✅ Statistical confidence in migration accuracy
- ✅ Automated validation reports

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

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

validate_example.sh

@@ -0,0 +1,61 @@
+#!/bin/bash
+# Example validation script
+# Demonstrates how to run Python processing and validate against MATLAB output
+
+set -e  # Exit on error
+
+# Configuration
+CONTROL_UNIT="CU001"
+CHAIN="A"
+OUTPUT_DIR="validation_reports"
+DATE=$(date +%Y-%m-%d_%H-%M-%S)
+
+echo "========================================"
+echo "Python vs MATLAB Validation Script"
+echo "========================================"
+echo "Control Unit: $CONTROL_UNIT"
+echo "Chain: $CHAIN"
+echo "Date: $DATE"
+echo ""
+
+# Create output directory
+mkdir -p "$OUTPUT_DIR"
+
+# Step 1: Run Python processing
+echo "Step 1: Running Python processing..."
+python -m src.main "$CONTROL_UNIT" "$CHAIN"
+echo "✓ Python processing complete"
+echo ""
+
+# Step 2: Wait a moment for database commit
+sleep 2
+
+# Step 3: Run validation for all sensor types
+echo "Step 2: Running validation..."
+REPORT_FILE="$OUTPUT_DIR/${CONTROL_UNIT}_${CHAIN}_validation_${DATE}.txt"
+
+python -m src.validation.cli "$CONTROL_UNIT" "$CHAIN" \
+    --output "$REPORT_FILE" \
+    --include-equivalent
+
+echo "✓ Validation complete"
+echo ""
+
+# Step 4: Display summary
+echo "========================================"
+echo "Validation Summary"
+echo "========================================"
+cat "$REPORT_FILE"
+echo ""
+
+echo "Full report saved to: $REPORT_FILE"
+
+# Check if validation passed
+if grep -q "VALIDATION PASSED" "$REPORT_FILE"; then
+    echo "✓✓✓ SUCCESS: Python output matches MATLAB ✓✓✓"
+    exit 0
+else
+    echo "✗✗✗ WARNING: Validation detected differences ✗✗✗"
+    echo "Please review the report above for details."
+    exit 1
+fi