feat: add versioned migrations and kysely query layer

backend/migrations/1700000004000_create-trip-settings.cjs

@@ -0,0 +1,23 @@
+exports.up = (pgm) => {
+  pgm.createTable('trip_settings', {
+    trip_id: {
+      type: 'uuid',
+      primaryKey: true,
+      notNull: true,
+      references: 'trips(id)',
+      onDelete: 'CASCADE',
+    },
+    web_research_enabled: { type: 'boolean', notNull: true, default: false },
+    periodic_agent_review_enabled: { type: 'boolean', notNull: true, default: false },
+    notification_email_enabled: { type: 'boolean', notNull: true, default: true },
+    notification_push_enabled: { type: 'boolean', notNull: true, default: true },
+    default_research_depth: { type: 'text' },
+    default_planning_style: { type: 'text' },
+    created_at: { type: 'timestamptz', notNull: true, default: pgm.func('now()') },
+    updated_at: { type: 'timestamptz', notNull: true, default: pgm.func('now()') },
+  });
+};
+
+exports.down = (pgm) => {
+  pgm.dropTable('trip_settings');
+};