Add test coverage reporting and improve coverage to 80%+

[RonaldRonnie]

Description:
Test coverage is not currently measured or reported. Need to add coverage reporting and improve coverage to meet production standards (80%+).

Expected Behavior:

• Add pytest-cov for coverage reporting
• Configure coverage to exclude tests and setup files
• Set minimum coverage threshold (80%)
• Add coverage badge to README
• Generate coverage reports in CI

Impact:

• Unknown code quality
• Potential bugs in production
• No visibility into untested code

Acceptance Criteria:

• pytest-cov added to dev dependencies
• Coverage configuration added (.coveragerc or pyproject.toml)
• Coverage badge added to README
• CI generates coverage reports
• Coverage threshold enforced (fail if below 80%)
• Coverage report shows which files need more tests

Current State:

• Tests exist in tests/ directory
• No coverage measurement configured