MainsKeeper Battery Assurance 0.2.1 — source-only correction review

Archives
- mainskeeper-app-checkpoint-0.2.1.zip (patch from 0.2.0)
- mainskeeper-app-0.2.1.zip (patch from 0.2.0)
Authored payload: 523 files, matching between checkpoint and handoff.
Prior 0.2.0 archives preserved.

Verification performed
- node --check on changed modules: pass
- node product/app/assets/state-checks.js --quiet: PASS · 246 passed · 0 failed
- node product/cli/build-examples.js: wrote 154 files; assurance screens/JSON retained
- ZIP CRC/integrity: pass; SHA-256 reported at packaging time

Browser verification and screenshots skipped by user request.
Visual and browser-interaction acceptance remain unverified.
