fix: address 10 codebase audit findings — API guards, reconcile, merge fallback, tracker guards

- immich_api: guard resp.json() with isinstance(dict) check in get_people and
  fetch_all_assets so AttributeError doesn't escape on proxy/CDN non-dict responses
- executor: move actually_uploaded.append outside try/else so Frigate filename→asset_id
  mapping is created via reconcile even when the tracker write fails
- cli: fall back to pre-merge people list when re-fetch after merge returns empty
  (transient error) instead of silently dropping all people
- cli: treat ENABLE_FRIGATE_SCORES=false / BLUR_THRESHOLD=0 as not-set in
  the unsupported-vars warning (falsy string check replaces raw truthiness)
- upload_tracker: guard set(data[flat_key]) with isinstance(list) check in
  reset_person so a corrupted non-iterable legacy field doesn't crash mid-reset
- upload_tracker: guard dims[0]/dims[1] in find_by_crop_dimension with a
  length check so a truncated crop_dims entry doesn't raise IndexError
- cache: wrap os.remove() in clear() with try/except OSError to handle
  TOCTOU race with concurrent put() calls
- diversity: default conf_array to 0.5 (was 1.0) for faces with missing
  confidence so they receive a moderate diversity boost instead of being
  treated as high-confidence
- diversity: sort assets in the fast path (len <= limit) so return order is
  consistent with the sorted-by-fileCreatedAt path

winnow/cache.py

@@ -103,8 +103,11 @@ class EmbeddingCache:
         count = 0
         for f in os.listdir(self.cache_dir):
             if f.endswith(".npy"):
-                os.remove(os.path.join(self.cache_dir, f))
-                count += 1
+                try:
+                    os.remove(os.path.join(self.cache_dir, f))
+                    count += 1
+                except OSError:
+                    pass
         logger.info("Cleared %s cached embeddings.", count)