perf(ebook-search): run phrase detection in parallel with retrieval

Move protected phrase detection into the retrieval gather so it runs
concurrently with vector and BM25 candidates instead of sequentially
before them. Make the search API accept real bool form fields for
rerank/phrase_matching, gate phrase matching on both the request and
config kill switch, and reflow log f-strings for readability.

python/ebook_search/protected_phrases/generate_ngrams.py

@@ -68,8 +68,8 @@ async def generate_candidate_phrases_for_books(
         source_ids = (await session.scalars(source_query)).all()
     books_seen = len(source_ids)
     logger.info(
-        f"ebook_candidate_phrase_generation_start {books_seen=} {config.phrase_min_tokens=} {config.phrase_max_tokens=} "
-        f"{config.protected_phrase_max_candidates_per_book=}"
+        f"ebook_candidate_phrase_generation_start {books_seen=} {config.phrase_min_tokens=} "
+        f"{config.phrase_max_tokens=} {config.protected_phrase_max_candidates_per_book=}"
     )
 
     pool = get_extraction_pool(config.protected_phrase_extraction_workers)
@@ -244,8 +244,8 @@ async def generate_candidate_phrases_for_book(
         await session.rollback()
         raise
     logger.info(
-        f"ebook_candidate_phrase_generation_book_duration {book_id=} {saved_count=} duration_ms={(perf_counter() - "
-        f"started_at) * 1000:.1f}"
+        f"ebook_candidate_phrase_generation_book_duration {book_id=} {saved_count=} "
+        f"duration_ms={(perf_counter() - started_at) * 1000:.1f}"
     )
     return saved_count
 
@@ -289,7 +289,7 @@ async def store_candidate_phrases_for_book(
         )
         saved_count = await bulk_upsert_unjudged_candidates(session, book_id, series_id, limited_candidates)
     logger.info(
-        f"ebook_candidate_phrase_save_complete {book_id=} {saved_count=} save_ms={(perf_counter() - save_started_at) * "
-        f"1000:.1f}"
+        f"ebook_candidate_phrase_save_complete {book_id=} {saved_count=} "
+        f"save_ms={(perf_counter() - save_started_at) * 1000:.1f}"
     )
     return saved_count