feat: Support STRUCTKIT_STRUCTURES_PATH environment variable (#122)

[httpdss]

Description

This PR implements support for the STRUCTKIT_STRUCTURES_PATH environment variable to address #122.

Changes

• Add environment variable support: Users can now set STRUCTKIT_STRUCTURES_PATH to specify a default structures path without repeating the -s flag on every command
• Precedence: Command-line arguments take precedence over environment variables (consistent with existing patterns)
• Logging: When the environment variable is used, a log message is emitted for transparency
• Testing: Comprehensive test suite covering all precedence scenarios
• Documentation: Updated CLI reference with environment variables section and generate command documentation

Implementation Details

• Modified GenerateCommand.execute() to check for STRUCTKIT_STRUCTURES_PATH environment variable when --structures-path is not provided
• Follows the existing pattern used by STRUCTKIT_LOG_LEVEL
• All tests pass successfully

Usage Example

export STRUCTKIT_STRUCTURES_PATH=~/custom-structures
structkit generate python-basic ./my-project
# Equivalent to: structkit generate -s ~/custom-structures python-basic ./my-project

Testing

• ✅ 5 new tests covering:

  • Environment variable is used when no CLI arg provided
  • CLI argument takes precedence over environment variable
  • No structures path when env var not set
  • Logging message is emitted
  • Empty env var is ignored

• ✅ All existing tests continue to pass

• ✅ Pre-commit hooks pass (formatting, linting)

Closes

Closes #122

[Copilot]

Pull Request Overview

This PR adds support for the STRUCTKIT_STRUCTURES_PATH environment variable to provide a convenient way to set a default structures path without repeating the -s flag on every command.

• Environment variable support with proper CLI precedence (command-line arguments override environment variables)
• Logging transparency when the environment variable is used
• Comprehensive test coverage for all precedence scenarios

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
tests/test_env_var_structures_path.py	Comprehensive test suite covering environment variable precedence, CLI override, logging, and edge cases
structkit/commands/generate.py	Implementation of environment variable resolution logic in the execute method
docs/cli-reference.md	Updated documentation with environment variables section and usage examples