Merge wr/release-readiness-audit-fixes: audit fixes, 0.1.5

Resolves all findings from the pre-release audit:

- Fix parseGoalArguments: dangling/adjacent flags no longer corrupt the
  goal condition
- Fix /goal resume: no-op with clear message when goal is already running
- Fix system.transform: filter(Boolean) before join removes trailing
  newline when no warnings apply
- Remove live Map refs from testInternals
- Raise default maxDurationMs from 5 min to 15 min so the turn limit is
  the binding brake at typical LLM latency
- Add 12 new tests (error paths, multi-session, flag edge cases, cleanup)
- Rewrite README: limits table, effective-turn-count note, per-goal flags
  table, updated config examples
- Add node >=18 engine constraint, author email, *.tgz to .gitignore
- Bump to 0.1.5