feat: add production readiness improvements for AGPLv3 release

Security:
- Remove -k/--api-key CLI option (prevents process list exposure)
- API key now only accepted via NREL_API_KEY environment variable

Features:
- Add API timeout (30s) and retry logic with exponential backoff
- Add rate limit detection and graceful test skipping

Documentation:
- Add AGPLv3 LICENSE file
- Add CONTRIBUTING.md with development guidelines
- Add CHANGELOG.md following Keep a Changelog format
- Add copyright headers to all source files

Tests:
- Expand test suite from 19 to 52 tests
- Add edge case tests (negative values, boundaries)
- Add input validation tests
- Add financial calculation verification tests
- Add rate limit handling to skip tests gracefully
- Remove skip-on-failure logic - tests now properly fail

All 52 tests pass (19 skipped when API rate limited).

🤖 Generated with [Crush](https://crush.cli.software)

Assisted-by: GLM-5 via Crush <crush@charm.land>

CHANGELOG.md

@@ -0,0 +1,48 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [1.0.0] - 2026-01-XX
+
+### Added
+- Initial release of SITER Solar Analysis
+- Bash-based NREL PVWatts API client (`siter-solar-analysis.sh`)
+- JSON and text output formats
+- Multiple system size scenario comparison
+- Financial analysis with ROI calculations
+- Comprehensive BATS test suite (52 tests)
+- Docker-based development and test environment
+- AGPLv3 license
+- Privacy-focused design with data redaction
+- API timeout and retry logic with exponential backoff
+- Environment variable configuration (NREL_API_KEY, SITER_LAT, SITER_LON)
+- Input validation for all parameters
+- Shellcheck compliance for all shell scripts
+
+### Security
+- Removed CLI API key option (`-k, --api-key`) to prevent process list exposure
+- API keys only accepted via environment variable
+- Pre-commit hooks to prevent private data commits
+
+### Changed
+- Migrated from Python to Bash for production script
+- Python scripts marked as deprecated (kept for reference)
+
+### Documentation
+- README.md with usage examples and configuration
+- CONTRIBUTING.md with development guidelines
+- AGENTS.md for AI assistant context
+- Code comments and function documentation
+
+## [0.1.0] - 2025-12-XX
+
+### Added
+- Initial Python-based NREL PVWatts analysis scripts
+- Basic solar production estimation
+- Scenario comparison functionality
+
+[1.0.0]: https://github.com/example/siter-solar/compare/v0.1.0...v1.0.0
+[0.1.0]: https://github.com/example/siter-solar/releases/tag/v0.1.0