refactor: unify env var helpers and remove magic slice in cache

- Add _getenv_num as shared core for _getenv_int/_getenv_float
- Add _getenv_optional_float for FRIGATE_SCORE_CEILING (replaces 9-line inline block)
- Add _getenv_bool; replace 11 inline .lower()-in-("true","1","yes") sites
  across config.py, jobs.py, and cli.py with single call site
- _resolve_strategy no-embedding branch: inline try/except → _getenv_int("LIMIT", 30)
- cache.py: final[:-4] → final.removesuffix(".npy") — assumption is now explicit

winnow/cache.py

@@ -85,7 +85,7 @@ class EmbeddingCache:
         final = self._path(asset_id, model)
         # Insert .tmp before .npy so np.save doesn't auto-append another .npy extension
         # (np.save appends .npy to paths that don't already end in .npy).
-        tmp = final[:-4] + ".tmp.npy"
+        tmp = final.removesuffix(".npy") + ".tmp.npy"
         try:
             np.save(tmp, embedding)
             os.replace(tmp, final)