feat: add versioned migrations and kysely query layer

backend/migrations/1700000005000_create-trip-members.cjs

@@ -0,0 +1,25 @@
+exports.up = (pgm) => {
+  pgm.createTable('trip_members', {
+    id: { type: 'uuid', primaryKey: true, default: pgm.func('gen_random_uuid()') },
+    trip_id: { type: 'uuid', notNull: true, references: 'trips(id)', onDelete: 'CASCADE' },
+    user_id: { type: 'uuid', notNull: true, references: 'users(id)' },
+    role: { type: 'text', notNull: true },
+    status: { type: 'text', notNull: true },
+    joined_at: { type: 'timestamptz' },
+    created_at: { type: 'timestamptz', notNull: true, default: pgm.func('now()') },
+    updated_at: { type: 'timestamptz', notNull: true, default: pgm.func('now()') },
+  });
+  pgm.addConstraint('trip_members', 'trip_members_trip_user_key', 'UNIQUE(trip_id, user_id)');
+  pgm.addConstraint('trip_members', 'trip_members_role_check', "CHECK (role IN ('OWNER','MEMBER'))");
+  pgm.addConstraint(
+    'trip_members',
+    'trip_members_status_check',
+    "CHECK (status IN ('INVITED','ACTIVE','DECLINED'))",
+  );
+  pgm.createIndex('trip_members', 'trip_id');
+  pgm.createIndex('trip_members', 'user_id');
+};
+
+exports.down = (pgm) => {
+  pgm.dropTable('trip_members');
+};