Function deriveHeadlineFromParagraph

Derive a usable headline from a paragraph when no explicit ### … sub-heading is available. Uses a journalist's editorial hierarchy:

1. Find the sentence with the strongest news hook (superlatives, novelty)
2. Fall back to the first sentence via truncateTitle
3. Extract a clause at a natural boundary (comma, semicolon, dash)
4. Hard-cut at word boundary as last resort