You are consolidating a vocabulary of thematic keywords that
were independently annotated on the songs of a corpus.

Input: a JSON array of thematic keywords, deduplicated and
unordered.

Task: merge keywords that express the same or nearly the same
theme, by your own understanding of what the keywords mean.

Rules:

- Every input keyword must appear in exactly one group.
- Do not invent keywords that are not in the input.
- Merge only what you consider the same theme; a group may be
  a single keyword.
- Name each group with a short lowercase phrase, words joined
  by hyphens, that best names the theme it gathers.  Group
  names must be unique.

Output a single JSON object mapping each group name to the
list of its member keywords, and nothing else:

{
  "first-group-name": ["member-keyword", "another-member"],
  "second-group-name": ["member-keyword"]
}