Clean up duplicate experience

Shows a preview of proposed merges and removals before anything changes — nothing is deleted automatically, and Apply only ever commits that dedup/merge decision. While it's at it, this pass also drafts a Role Description for any entry that doesn't have one yet — those never get written automatically, since it's free text you haven't read yet: each drafted description shows up right on its own card below, with its own Accept or Dismiss. Once you apply or dismiss the result, it also writes suggested Highlights for every job that has bullets but no highlights yet, each waiting on its card for your review. For combining two specific entries yourself, bullet by bullet, use the merge icon on an experience card instead.