WOTD _polish: enforce the "examples must use the word" contract

Per Codex audit: only accept a polish when there's a gloss AND at least one
example sentence that actually contains the word (case-insensitive). Examples
that don't use the word are dropped; if none remain, fall back to the raw
dictionary def/examples instead of shipping a gloss with empty/irrelevant usage.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

goodnews/wotd.py

@@ -95,7 +95,10 @@ def _polish(client, word: str, part_of_speech: str | None, definition: str) -> d
         return None
     gloss = " ".join(str(data.get("gloss") or "").split()).strip()
     examples = [" ".join(str(e).split()).strip() for e in (data.get("examples") or []) if str(e).strip()]
-    if not gloss:
+    # Enforce the contract: keep only sentences that actually use the word, and require at
+    # least one. A gloss with no usable examples falls back to the raw dictionary data.
+    examples = [e for e in examples if word.lower() in e.lower()]
+    if not gloss or not examples:
         return None
     return {"gloss": gloss, "examples": examples[:2]}