fix(pricing): fix grace_months form validation blocking submit when hidden

The hidden input had min=1 with value=0, causing browser validation error
"not focusable" when form submits. Changed to min=0 with empty default.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Modules/Pricing/Views/board_offers/form.php

@@ -164,7 +164,7 @@ $hasInstPath = !empty($old['has_inst_path']) || ($offer && ($offer['inst_months'
                         </div>
                         <div class="form-group" id="grace_months_group" style="<?= $v('inst_grace_type') ? '' : 'display:none;' ?>">
                             <label class="form-label">أشهر السماح</label>
-                            <input type="number" name="inst_grace_months" value="<?= $v('inst_grace_months', 0) ?>" class="form-input" min="1" max="60" style="direction:ltr;text-align:left;" placeholder="6">
+                            <input type="number" name="inst_grace_months" value="<?= $v('inst_grace_months') ?: '' ?>" class="form-input" min="0" max="60" style="direction:ltr;text-align:left;" placeholder="6">
                         </div>
                         <div class="form-group" id="post_grace_rate_group" style="<?= $v('inst_grace_type') === 'first_n_months' ? '' : 'display:none;' ?>">
                             <label class="form-label">فائدة بعد السماح (%)</label>