parse_instinct_file() was appending the instinct and resetting state
when frontmatter ended (second ---), before any content lines could be
collected. This caused all content (Action, Evidence, Examples) to be
lost during import.
Fix: only set in_frontmatter=False when frontmatter ends. The existing
logic at the start of next frontmatter (or EOF) correctly appends the
instinct with its collected content.
Fixes#148
