docs: add runner refresh ADR and plan

[mostlydev]

Summary

• add ADR-024 for refreshing built-in runner bases from upstream sources via claw pull
• add the implementation plan for issue Make runner updates intuitive and deterministic #128, including provenance, FROM rewriting, and drift detection
• preserve existing Clawfile authoring behavior by making single-Clawfile refresh reuse the same path-resolution rules as claw build <path>

Notes

• this keeps the trust model local: runner bases are rebuilt from upstream on the operator's machine rather than pulled as mostlydev-published harness images
• the competing ADR/plan drafts were intentionally not carried forward into this branch

Refs #128