v0.15.0 — Duplicate-merge assist in admin review queue

Flags pending items whose title is a close-but-not-auto-blocked match
against another pending or approved item in the same category — the
"near-miss" band the discovery pipeline's own dedup (0.85 fuzzy
threshold) doesn't catch, since anything at or above that threshold
never reaches the queue at all. Pure client-side string comparison
against already-fetched data, no schema change, no new dependency.

Verified against live data (read-only): correctly flagged 3 real
"Free Scholarship Test on X" listings from the same organization as
69-74% similar without claiming they're the same opportunity — exactly
the intended "worth a human glance" signal, not an auto-reject.