feat(ebook-search): implement async phrase matching for chunks and add ChunkPhraseHit model

python/ebook_search/protected_phrases/models.py

@@ -131,6 +131,21 @@ class PhraseMatch:
     series_id: int | None = None
 
 
+@dataclass(frozen=True, slots=True)
+class ChunkPhraseHit:
+    """One protected phrase with its mention count inside one retrieved chunk.
+
+    Attributes:
+        phrase_id (int): Protected phrase id.
+        phrase_text (str): Display text for the phrase.
+        mention_count (int): Indexed mentions inside the chunk.
+    """
+
+    phrase_id: int
+    phrase_text: str
+    mention_count: int
+
+
 @dataclass(frozen=True, slots=True)
 class PhraseCandidateGenerationResult:
     """Summary of candidate phrase extraction for indexed books.