fix: pagination runaway, double iteration, and reconciliation efficiency (#30)

immich_api.py:
- Move empty-page break after non-dict filtering — a page of all-null
  items no longer loops to MAX_PAGES without terminating
- Single-pass partition replaces two inverse isinstance scans per page
- Upgrade non-dict item log from DEBUG to WARNING (silent asset loss)

reconcile.py:
- Check Frigate before the first sleep so fast responses return
  immediately rather than always paying a 1 s delay
- Compute set difference once per poll iteration instead of twice

Bump version to 0.5.6

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "winnow"
-version = "0.5.5"
+version = "0.5.6"
 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"