release: v0.5.15 — fix cache regression and structural cleanup

- cache.py: fix np.save extension bug from v0.5.13 — tmp path used
  final+".tmp" (abc.npy.tmp) but np.save auto-appends .npy to paths not
  ending in .npy, writing to abc.npy.tmp.npy instead; os.replace then
  raised FileNotFoundError silently, making every cache write a no-op
  and leaking *.npy.tmp.npy files. Fixed by inserting .tmp before .npy:
  tmp = final[:-4] + ".tmp.npy"

- config.py: remove str(default) round-trip in _getenv_int/_getenv_float
  — use raw = os.getenv(name); return default if raw is None else int(raw)
  so a future float default can't cause a spurious "not a valid integer"
  warning and return the wrong type

- executor.py: consolidate 4 progress.remove_task calls into one
  try/finally around the per-job body; continue inside try/finally
  executes the finally before the next iteration, making the invariant
  structurally enforced rather than relying on discipline across 4 sites

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "winnow"
-version = "0.5.14"
+version = "0.5.15"
 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"