feat: add model_usage table and tracker methods

Adds model_usage schema, record_model_usage(), get_raw_model_stats(), and get_model_stats() to UsageTracker, with reset() support and 8 passing tests.

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

tests/test_model_tracker.py

@@ -0,0 +1,74 @@
+import pytest
+import tempfile
+import os
+from tracker import UsageTracker
+
+
+@pytest.fixture
+def tracker(tmp_path):
+    return UsageTracker(db_path=str(tmp_path / "test.db"))
+
+
+def test_record_and_retrieve_model_usage(tracker):
+    tracker.record_model_usage([("dreamshaper.safetensors", "checkpoints")])
+    tracker.record_model_usage([("dreamshaper.safetensors", "checkpoints")])
+
+    raw = tracker.get_raw_model_stats()
+    assert len(raw) == 1
+    assert raw[0]["model_name"] == "dreamshaper.safetensors"
+    assert raw[0]["model_type"] == "checkpoints"
+    assert raw[0]["count"] == 2
+
+
+def test_record_multiple_models(tracker):
+    tracker.record_model_usage([
+        ("dreamshaper.safetensors", "checkpoints"),
+        ("vae.safetensors", "vae"),
+    ])
+    raw = tracker.get_raw_model_stats()
+    assert len(raw) == 2
+
+
+def test_reset_clears_model_usage(tracker):
+    tracker.record_model_usage([("model.safetensors", "checkpoints")])
+    tracker.reset()
+    assert tracker.get_raw_model_stats() == []
+
+
+def test_empty_models_returns_empty(tracker):
+    assert tracker.get_raw_model_stats() == []
+
+
+def test_get_model_stats_used(tracker):
+    tracker.record_model_usage([("model.safetensors", "checkpoints")])
+    installed = {"checkpoints": ["model.safetensors"]}
+    result = tracker.get_model_stats(installed)
+    assert len(result) == 1
+    assert result[0]["model_type"] == "checkpoints"
+    assert result[0]["models"][0]["status"] == "used"
+    assert result[0]["models"][0]["count"] == 1
+
+
+def test_get_model_stats_never_used_new(tracker):
+    installed = {"checkpoints": ["unused.safetensors"]}
+    result = tracker.get_model_stats(installed)
+    assert result[0]["models"][0]["status"] == "unused_new"
+    assert result[0]["models"][0]["count"] == 0
+
+
+def test_get_model_stats_uninstalled(tracker):
+    tracker.record_model_usage([("gone.safetensors", "checkpoints")])
+    installed = {}  # no longer on disk
+    result = tracker.get_model_stats(installed)
+    assert result[0]["models"][0]["status"] == "uninstalled"
+    assert result[0]["models"][0]["installed"] is False
+
+
+def test_get_model_stats_sorted_by_status(tracker):
+    tracker.record_model_usage([("active.safetensors", "checkpoints")])
+    installed = {"checkpoints": ["active.safetensors", "unused.safetensors"]}
+    result = tracker.get_model_stats(installed)
+    models = result[0]["models"]
+    statuses = [m["status"] for m in models]
+    # unused_new (2) comes before used (3) in STATUS_ORDER
+    assert statuses.index("unused_new") < statuses.index("used")