Establish isolated mutation execution foundation

[greenthree]

Summary

• capture one immutable problem baseline under the workspace build lock
• execute mutants in independent temporary workers with serial deterministic ordering
• release the global build lock during long Judge runs while retaining final live-input fencing
• forward bounded memory, process, output and cancellation controls through Judge
• add optional, strictly validated execution profile data to mutation evidence with v2 compatibility
• centralize consistent problem snapshot copying for checkpoint/generation/mutation

Validation

• npm run check (720 passed, 30 skipped)
• npm run pack:check (probhub=224 files, probhub-skill=5 files)
• python -X utf8 C:\\Users\\13952\\.codex\\skills\\.system\\skill-creator\\scripts\\quick_validate.py .
• phtest: nine-problem --json lint passed
• git diff --check

P0 deliberately remains serial; --jobs and cross-problem parallel scheduling are deferred to the ROADMAP.