fix: correct reconcile log severity, docstring gaps, and _entry allocation (v0.5.9)

- reconcile.py: swap log levels — external-upload path (permanent mapping
  loss) escalated to WARNING; timeout path (transient, retries next cycle)
  downgraded to INFO. Also extend the warning message to note the files are
  permanently unmapped.

- immich_api.py: extend fetch_all_assets docstring to document that
  all-garbage page termination (in addition to network errors) makes
  total_raw a lower bound.

- executor.py: add comment above shutil.rmtree noting that POSIX rmtree
  raises NotADirectoryError on a top-level symlink, documenting why the
  removed islink guard is safe to omit.

- upload_tracker.py: replace setdefault with explicit guard in _entry() —
  setdefault evaluates its default-dict argument before checking key
  presence, allocating and discarding a dict on every already-present call.

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "winnow"
-version = "0.5.8"
+version = "0.5.9"
 description = "Selects diverse, high-quality photos from Immich as training data for Frigate face recognition."
 license = "AGPL-3.0-or-later"
 requires-python = ">=3.13"