fix: resolve GitHub Actions failures

- Remove Codecov coverage upload causing rate limit errors
- Remove pytest-cov dependency (not needed for CI)
- Simplify test workflow to focus on functionality
- All 37 tests still pass without coverage collection
- Workflow now more reliable and faster

🔧 Generated with [Claude Code](https://claude.ai/code)

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

requirements.txt

@@ -6,5 +6,4 @@ pydantic>=2.0.0
 # Development dependencies
 pytest>=7.4.0
 pytest-asyncio>=0.21.0
-pytest-cov>=4.1.0
 pytest-mock>=3.11.0