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>

.gitignore

@@ -1 +1,29 @@
-home/*
+# Project directories
+home/*
+
+# Environment variables (contains sensitive data)
+.env
+
+# Python cache
+__pycache__/
+*.pyc
+*.pyo
+*.pyd
+.Python
+
+# Virtual environments
+venv/
+env/
+ENV/
+
+# IDEs
+.vscode/
+.idea/
+*.swp
+*.swo
+
+# Logs
+*.log
+
+# Database configuration (legacy)
+DB.txt