fix(rerank): ground entity-miss demotion on head token, not full phrase

The entity-grounding demotion required the full multi-word primary
entity as a contiguous substring, so on-entity items missing a trailing
search descriptor were buried: a 323-pt HN thread "Stripe is friendly
to 'friendly fraud'" scored 0 on a "Stripe payments" query. New
_entity_grounded helper keys on the brand head token; items that never
name the brand still miss it and stay demoted. reddit_keyless
_slot_priority, which had re-implemented the old check while claiming
to mirror rerank's signal, now calls the shared helper so the two
paths cannot diverge.

skills/last30days/scripts/lib/reddit_keyless.py

@@ -170,9 +170,11 @@ def _slot_priority(topic: str, posts: List[Dict[str, Any]]) -> List[Dict[str, An
     posts that rerank later demotes as entity misses starves the on-topic
     posts the user actually sees (2026-06-06 "OpenClaw vs Hermes" run:
     2,000+ upvote Gemma/GPU threads took every slot, then were demoted to
-    zero). Mirror rerank's demotion signal — the topic's stripped primary
-    entity contained in the post text — so slots go to posts likely to
-    survive final ranking. Falls back to token-overlap relevance when the
+    zero). Mirror rerank's demotion signal via the shared `_entity_grounded`
+    check (head token of the topic's stripped primary entity present in the
+    post text) so slots go to posts likely to survive final ranking — keying
+    on the same head token keeps the two paths from diverging. Falls back to
+    token-overlap relevance when the
     topic yields no usable primary entity. Within each tier the incoming
     (score-first) order is preserved. Never raises; on any failure the
     incoming order is returned unchanged.
@@ -186,7 +188,7 @@ def _slot_priority(topic: str, posts: List[Dict[str, Any]]) -> List[Dict[str, An
         entity = rerank._primary_entity(topic).lower()
         if entity:
             def _matches(post: Dict[str, Any]) -> bool:
-                return entity in _post_text(post).lower()
+                return rerank._entity_grounded(_post_text(post).lower(), entity)
         else:
             prepared = relevance.PreparedQuery(topic)