Add comprehensive E2E tests for materia CLI

- Add pytest and pytest-cov for testing
- Add niquests for modern HTTP/2 support (keep requests for hcloud compatibility)
- Create 13 E2E tests covering CLI, workers, pipelines, and secrets (71% coverage)
- Fix Pulumi ESC environment path (beanflows/prod) and secret key names
- Update GitLab CI to run CLI tests with coverage reporting

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

CLAUDE.md

@@ -201,3 +201,4 @@ GitLab CI runs three stages (`.gitlab-ci.yml`):
 
 Note: The dev database is large and should not be committed to git (.gitignore already configured).
 - We use a monorepo with uv workspaces
+- The pulumi env is called beanflows/prod