Read each candidate source, harvest its strongest bullets, and return them flattened in priority order with their originating run-relative path.
Absolute path to the analysis run directory
Ordered list of run-relative artifact paths to mine
Ordered candidate list (may exceed MAX_TAKEAWAYS; caller should call dedupeTakeaways before rendering)
Read each candidate source, harvest its strongest bullets, and return them flattened in priority order with their originating run-relative path.