fix: code review corrections — dedup O(N²), truncated rejection check, pool warning, path guard

- _dedup_embeddings: rebuild kept_stack only on keep (was every iteration → O(N²))
- _dedup_embeddings: fix quality_score sort key to use explicit None check (falsy-zero)
- _select_by_embedding: add post-dedup pool < limit guard with warning
- executor: use full resp.text for 'face' keyword check; only truncate display snippet
- _safe_person_dir: avoid false "//" prefix when output_dir resolves to filesystem root

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "winnow"
-version = "0.4.4"
+version = "0.4.5"
 description = "Selects diverse, high-quality photos from Immich as training data for Frigate face recognition and object classification."
 license = "AGPL-3.0-or-later"
 requires-python = ">=3.13"