fix: store opened_at and closed_at as DATETIME (not DATE)

DATE columns lose time information, causing timeline to show 00:00 for
car reception and WO closure. Migrated both columns to DATETIME and
updated: model casts (date → datetime), form pickers (DatePicker →
DateTimePicker with seconds:false), default to now() instead of today(),
and cleaned up defensive Carbon::parse() in getTimeline().

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

database/migrations/2026_09_11_110000_change_opened_closed_at_to_datetime.php

@@ -0,0 +1,23 @@
+<?php
+
+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('work_orders', function (Blueprint $table) {
+            $table->dateTime('opened_at')->nullable()->change();
+            $table->dateTime('closed_at')->nullable()->change();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('work_orders', function (Blueprint $table) {
+            $table->date('opened_at')->nullable()->change();
+            $table->date('closed_at')->nullable()->change();
+        });
+    }
+};