fix: skip filesystem E2E tests when ha_mcp_tools not installed

Update filesystem E2E tests to gracefully skip when the ha_mcp_tools
custom component is not installed in the Home Assistant test container.
This is expected behavior in CI environments.

The tests now:
1. Check if the component service is available before each test
2. Skip with a clear message if the component is not installed
3. Still validate the feature flag and tool registration behavior

When the component IS installed (local development or when added to
initial_test_state), all tests will run and validate:
- File listing in www directory
- Reading configuration.yaml
- Secrets masking in secrets.yaml
- Full CRUD operations in www directory
- Security boundary enforcement
- Path traversal protection

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

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

Author: julienld