fix(fusion_claims): force full-width dashboard sheet with dedicated class

The .o_fc_dashboard .o_form_sheet override wasn't winning specificity
against Odoo's default form-sheet constraints. Added a dedicated class
o_fc_dashboard_sheet directly on the <sheet> element + !important
overrides on max-width, width, and flex to stretch the sheet to the
full container width.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fusion_claims/views/dashboard_views.xml

@@ -6,7 +6,7 @@
         <field name="arch" type="xml">
             <form string="Dashboard" create="0" delete="0" edit="0"
                   class="o_fc_dashboard">
-                <sheet>
+                <sheet class="o_fc_dashboard_sheet">
 
                     <!-- Hidden invariants used by buttons + widgets -->
                     <field name="currency_id" invisible="1"/>