Add std_run command runner API

[codeforester]

Summary

• Add std_run as the preferred command-runner API.
• Keep run as a compatibility wrapper for existing callers.
• Update docs, examples, and stdlib tests to prefer std_run.

Validation

• RED: bats --filter "std_run is the preferred" lib/bash/std/tests/lib_std.bats failed before the fix because std_run was missing.
• GREEN: bats --filter "std_run is the preferred" lib/bash/std/tests/lib_std.bats passed after the fix.
• bats --filter "(std_run|run compatibility)" 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 examples/std-usage.sh
• ./tests/validate.sh
• git diff --check

Fixes #15