fix(write-path): a search hit's excerpt under snippet no longer 500s the prior-art route (#4768)

#4768 "Write-path prior-art route 500s when a nameless search hit carries
its excerpt under `snippet`": _prior_art_line read item["snippet"] as a
snippet record's field dict, but a search hit carries its matched passage
there as a string. Read the name only from a dict.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scribe/services/plugin_context.py

@@ -1698,8 +1698,11 @@ def _prior_art_line(item: dict, marker: str, owner: str | None, foreign_lang: st
     """
     # The NAME, not the composed title (#4364) — a snippet's title carries its
     # whole trigger and ran to kilobytes on this line, again on every repeat.
+    # `snippet` is a snippet record's field dict — but on a search hit it is
+    # the matched excerpt, a string, under the same key.
+    fields = item.get("snippet")
     title = (
-        item.get("name") or (item.get("snippet") or {}).get("name")
+        item.get("name") or (fields.get("name") if isinstance(fields, dict) else None)
         or (item.get("title") or "(untitled)")
     ).replace("\n", " ").strip()
     mark = f"{marker} · {foreign_lang}" if foreign_lang else marker