fix: rename agent_sessions columns to match model expectations

Renames uuid → session_id and last_activity_at → last_active_at,
and changes session_id column type from uuid to varchar to support
prefixed IDs (sess_...).

Co-Authored-By: Virgil <virgil@lethean.io>

Migrations/0001_01_01_000010_rename_session_columns.php

@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('agent_sessions', function (Blueprint $table) {
+            $table->renameColumn('uuid', 'session_id');
+            $table->renameColumn('last_activity_at', 'last_active_at');
+        });
+
+        // Change column type from uuid to string to allow prefixed IDs (sess_...)
+        Schema::table('agent_sessions', function (Blueprint $table) {
+            $table->string('session_id')->unique()->change();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('agent_sessions', function (Blueprint $table) {
+            $table->renameColumn('session_id', 'uuid');
+            $table->renameColumn('last_active_at', 'last_activity_at');
+        });
+    }
+};