feat: better chat support for thinking

migrations/20260724230000_create_messages/up.sql

@@ -0,0 +1,10 @@
+CREATE TABLE messages (
+    id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
+    session_id INTEGER NOT NULL REFERENCES sessions(id) ON DELETE CASCADE,
+    user BOOLEAN NOT NULL CHECK (user IN (0, 1)),
+    reasoning TEXT,
+    reasoning_complete BOOLEAN NOT NULL DEFAULT 1 CHECK (reasoning_complete IN (0, 1)),
+    content TEXT NOT NULL
+);
+
+CREATE INDEX messages_session_id ON messages(session_id);