- _getenv_num: add raw.strip() + empty-string guard so numeric vars set
to "" (common Compose pattern for "use default") return the default
silently instead of warning "not a valid int/float"
- _getenv_bool: same guard so True-defaulted flags set to "" return
the configured default instead of silently returning False
- embeddings.py: replace inline FORCE_CPU bool parse with _getenv_bool