Polish stdlib logging behavior

[codeforester]

Summary

• Respect NO_COLOR when initializing stdlib terminal colors.
• Compose structured log records before one final stderr write.
• Reuse bounded caller-location logic for file-log unknown-logger warnings.
• Document stdout/stderr behavior for print helpers and the NO_COLOR contract.

Validation

• RED: focused logging tests failed before the fix for the three new contracts.
• GREEN: bats --filter "(NO_COLOR|one final printf|file logging helpers)" lib/bash/std/tests/lib_std.bats
• bats --filter "(color initialization|NO_COLOR)" lib/bash/std/tests/lib_std.bats
• bats lib/bash/std/tests/lib_std.bats
• shellcheck --severity=error lib/bash/std/lib_std.sh lib/bash/std/tests/lib_std.bats
• git diff --check
• ./tests/validate.sh

Fixes #18