fix(logging): add runtime guard for unsafe logging methods

[chaliy]

Summary

Closes #1179

• unsafe_disable_redaction() and unsafe_log_scripts() now require BASHKIT_UNSAFE_LOGGING=1 env var to take effect
• Without the env var, both methods are no-ops and emit a warning to stderr
• When the env var is set, a warning is still emitted confirming unsafe logging is active
• Updated docs/logging.md to document the env var requirement

Test plan

• test_unsafe_methods_noop_without_env — verifies both methods are no-ops without env var
• test_disabled_redaction — verifies methods work with env var set
• test_script_formatting — verifies script logging works with env var
• All 8 unit tests and 26 integration tests pass