🌱 (alpha): Remove redundant alpha generate e2e tests

All test coverage already exists in comprehensive unit tests
at pkg/cli/alpha/internal/generate_test.go (48 specs covering
all PROJECT file fields, plugins, and edge cases).

Removed:
- test/e2e/alphagenerate/ directory
- alphagenerate e2e test execution from test/features.sh

Assisted-by: Cursor

Author: camilamacedo86