nuwiki defaulted the per-wiki diary_caption_level to 1; upstream vimwiki's
default is 0 (year captions at the top level, months one below, rather than
nested one deeper). Default it to 0 in wiki_defaults(); still per-wiki
overridable. Render tests pass an explicit level so are unaffected; the
default-value assertion in defaults_carry_vimwiki_per_wiki_keys updated.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
gffranco
28d5caf581