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>

app/Models/Tenant/WorkOrder.php

@@ -45,8 +45,8 @@ class WorkOrder extends Model implements HasMedia
     ];
 
     protected $casts = [
-        'opened_at' => 'date',
-        'closed_at' => 'date',
+        'opened_at' => 'datetime',
+        'closed_at' => 'datetime',
         'approved_at' => 'datetime',
         'eta_at' => 'datetime',
         'eta_promised' => 'datetime',