feat(collector): capture additional smartctl diagnostics

Record host read and write commands, controller busy time, error log
entries, warning and critical temperature time, and thermal management
transitions from the existing smartctl -a -j acquisition. Schema 7 adds
nullable columns to samples so legacy rows read as unknown, and the
Diagnostics panel shows each counter with its change.

tests/test_collector_history_tracer.py

@@ -154,7 +154,7 @@ class TestSchemaMigration:
 
         # Migrate
         steps = migrate_to_latest(db)
-        assert steps == 5  # v1→v2→v3→v4→v5→v6
+        assert steps == 6  # v1→v2→v3→v4→v5→v6→v7
 
         # Verify data preserved
         conn = sqlite3.connect(str(db))