Unify the config folder name to `.opencodereview` across all runtime paths,
tests, docs, and i18n strings. Also make defaultConfigPath() return an error
instead of silently falling back to a current-directory file when $HOME is
unresolvable.
Consolidate review rules into a composedResolver that supports four layers
(--rule flag > project .open-code-review/rule.json > global ~/rule.json >
embedded system default), each with first-match-wins fall-through semantics.
kite