feat: append-only event log with projector skeleton

tests/test_eventlog.py

@@ -0,0 +1,15 @@
+from chat.db.migrate import apply_migrations
+from chat.db.connection import open_db
+from chat.eventlog.log import append_event, read_events
+
+
+def test_append_and_read(tmp_path):
+    db = tmp_path / "t.db"
+    apply_migrations(db)
+    with open_db(db) as conn:
+        eid = append_event(conn, kind="test_kind", payload={"a": 1})
+        assert eid > 0
+        rows = list(read_events(conn))
+        assert len(rows) == 1
+        assert rows[0].kind == "test_kind"
+        assert rows[0].payload["a"] == 1