feat(runtime): migrate Base to base-bash-libs v2 API #1880

Tracking issue for the first-party Base cutover required by base-bash-libs roadmap #240.

Scope:

• migrate all Base Bash consumers to the v2 base_ API
• fix basectl help and explicit stdlib initialization
• update focused runtime and documentation coverage
• raise the minimum to v2.0.0 after the base-bash-libs GA asset is verified

The implementation is currently proposed in PR #1879.