Add quality replacement for Frigate face training images

When a person is at MAX_AUTO_IMAGES, winnow now replaces the
lowest-quality mapped training image in Frigate if a higher-confidence
candidate is available, keeping the training set always optimised.

Only files winnow uploaded (tracked via frigate_files mapping) are ever
replaced — manually added Frigate training images are never touched.
A concurrent-upload race condition is detected per-file: if N>1 new
files appear after one upload, the mapping is skipped rather than
guessed, logging at INFO level. The per-file snapshot approach is
retained over a batch approach because wrong mappings (which a batch
approach risks on race) are worse than no mapping.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_upload_tracker.py

@@ -69,3 +69,73 @@ def test_duplicate_marks_are_idempotent():
     mark_uploaded("dup", person_name="Alice")
     mark_uploaded("dup", person_name="Alice")
     assert filter_already_uploaded(["dup", "new"]) == ["new"]
+
+
+# ── frigate_files mapping ─────────────────────────────────────────────────────
+
+def test_record_and_remove_frigate_file():
+    from winnow.upload_tracker import get_person_summary, record_frigate_file, remove_frigate_file
+    record_frigate_file("Alice", "Alice-1000.webp", "asset-a1")
+    assert "Alice-1000.webp" in get_person_summary()["Alice"]["frigate_files"]
+    remove_frigate_file("Alice", "Alice-1000.webp")
+    assert "Alice-1000.webp" not in get_person_summary()["Alice"]["frigate_files"]
+
+
+def test_remove_nonexistent_frigate_file_is_safe():
+    from winnow.upload_tracker import remove_frigate_file
+    # Should not raise even if the file was never recorded
+    remove_frigate_file("Alice", "Alice-ghost.webp")
+
+
+def test_remove_frigate_file_does_not_unmark_asset():
+    """Deleting a Frigate file should not re-expose the source asset for upload."""
+    from winnow.upload_tracker import (
+        filter_already_uploaded,
+        mark_uploaded,
+        record_frigate_file,
+        remove_frigate_file,
+    )
+    mark_uploaded("asset-a1", person_name="Alice")
+    record_frigate_file("Alice", "Alice-1000.webp", "asset-a1")
+    remove_frigate_file("Alice", "Alice-1000.webp")
+    # Asset must still be excluded — it was deliberately replaced, not lost
+    assert filter_already_uploaded(["asset-a1"]) == []
+
+
+def test_get_lowest_quality_mapped_file_none_when_empty():
+    from winnow.upload_tracker import get_lowest_quality_mapped_file
+    assert get_lowest_quality_mapped_file("Alice") is None
+
+
+def test_get_lowest_quality_mapped_file_returns_lowest():
+    from winnow.upload_tracker import (
+        get_lowest_quality_mapped_file,
+        mark_uploaded,
+        record_frigate_file,
+    )
+    mark_uploaded("asset-hi", person_name="Alice", score=0.95)
+    mark_uploaded("asset-lo", person_name="Alice", score=0.71)
+    record_frigate_file("Alice", "Alice-1000.webp", "asset-hi")
+    record_frigate_file("Alice", "Alice-1001.webp", "asset-lo")
+    result = get_lowest_quality_mapped_file("Alice")
+    assert result is not None
+    frigate_filename, asset_id, score = result
+    assert frigate_filename == "Alice-1001.webp"
+    assert asset_id == "asset-lo"
+    assert score == pytest.approx(0.71, abs=0.001)
+
+
+def test_get_lowest_quality_mapped_file_skips_unscored():
+    """Files mapped without a score should not be returned as candidates."""
+    from winnow.upload_tracker import (
+        get_lowest_quality_mapped_file,
+        mark_uploaded,
+        record_frigate_file,
+    )
+    mark_uploaded("asset-scored", person_name="Alice", score=0.85)
+    mark_uploaded("asset-noscr", person_name="Alice")
+    record_frigate_file("Alice", "Alice-1000.webp", "asset-scored")
+    record_frigate_file("Alice", "Alice-1001.webp", "asset-noscr")
+    result = get_lowest_quality_mapped_file("Alice")
+    assert result is not None
+    assert result[1] == "asset-scored"  # only scored file is a candidate