fix: reference projects(guid) not projects(id) in chat_histories FK

migrations/018_chat_histories.sql

@@ -7,7 +7,7 @@ CREATE TABLE IF NOT EXISTS chat_histories (
     title       TEXT,
     channel     TEXT,
     agent_id    TEXT,
-    project_id  UUID        REFERENCES projects(id) ON DELETE SET NULL,
+    project_id  UUID        REFERENCES projects(guid) ON DELETE SET NULL,
     messages    JSONB       NOT NULL DEFAULT '[]',
     summary     TEXT,
     metadata    JSONB       NOT NULL DEFAULT '{}',