* feat(ui): track frontend lint counts in a committed snapshot
Persist the eslint budget-rule counts (no-explicit-any, complexity,
max-depth) to eslint-metrics.json so the trend is queryable straight
from git history and can later feed a dashboard. A CI drift check
regenerated from the same lint report keeps the snapshot honest, so a
PR that shifts a count has to run npm run lint:metrics and commit it
* fix(ui): harden lint-metrics drift check and eslint failure handling
Make the drift comparison symmetric over the union of committed and
actual keys so a phantom rule left in eslint-metrics.json (for example
after a rule is dropped from eslint-budgets.json) is caught instead of
silently passing. Only swallow eslint's lint-errors exit code in the
generator and rethrow anything else, so a fatal eslint failure surfaces
its real output rather than a confusing ENOENT on the missing report
