Label blank account option "(None)" when no company default is set

The item account dropdowns showed "(Default … account)" on the blank
option even when the company hadn't configured a default — implying a
fallback that didn't exist. Now the blank option reads "(None)" unless a
matching company default is configured, in which case it keeps the
"(Default …)" label (the dropdown pre-selects the real account anyway).
"Has default" flags are computed in the shared dropdown-population helpers
so every render path (Create/Edit GET and invalid-POST) gets them.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/PowderCoating.Web/Views/CatalogItems/Create.cshtml

@@ -131,7 +131,7 @@
                             <div class="col-md-6 mb-3">
                                 <label asp-for="RevenueAccountId" class="form-label"></label>
                                 <select asp-for="RevenueAccountId" class="form-select" asp-items="ViewBag.RevenueAccounts">
-                                    <option value="">(Default revenue account)</option>
+                                    <option value="">@((ViewBag.HasDefaultRevenueAccount ?? false) ? "(Default revenue account)" : "(None)")</option>
                                 </select>
                                 <small class="form-text text-muted">Account credited when this item is invoiced.</small>
                             </div>
@@ -139,7 +139,7 @@
                                 <label asp-for="CogsAccountId" class="form-label"></label>
                                 <select asp-for="CogsAccountId" class="form-select" asp-items="ViewBag.CogsAccounts"
                                         data-quick-add-url="/Accounts/Create?preSubType=40" data-quick-add-title="Add COGS Account">
-                                    <option value="">(Default COGS account)</option>
+                                    <option value="">@((ViewBag.HasDefaultCogsAccount ?? false) ? "(Default COGS account)" : "(None)")</option>
                                     <option value="__new__">+ Add New Account&hellip;</option>
                                 </select>
                                 <small class="form-text text-muted">Account debited when materials are consumed.</small>