Add Custom Formula Item Templates with AI generation and wizard integration

Introduces per-company reusable NCalc2 pricing formula templates for complex
fabricated items (roof curbs, enclosures, welded frames). Templates support
two output modes — FixedRate (formula yields a dollar amount) and SurfaceAreaSqFt
(formula yields sq ft fed into the standard coating engine). Includes:

- CustomItemTemplate entity, migration (AddCustomItemTemplates), IUnitOfWork repo
- IsCustomFormulaItem / CustomItemTemplateId / FormulaFieldValuesJson flags on
  QuoteItem, JobItem, CreateQuoteItemDto; mapped in all 3 JobItemAssemblyService
  overloads and all existingItemsData JSON projections + pageMeta blocks
- ICustomFormulaAiService / CustomFormulaAiService: Claude-powered formula
  generator (natural language + optional diagram image) and NCalc2 evaluator
- CompanySettings CRUD endpoints: GetCustomItemTemplates, Create/Update/Delete,
  UploadTemplateDiagram, TemplateDiagram (blob serve), EvaluateFormula, GenerateFormulaFromAi
- Company Settings "Custom Formulas" tab + cfModal + company-settings-custom-formulas.js
- item-wizard.js: formula item type card, renderFormulaFields, wzFormulaRecalc
  (live evaluate via POST), collectStep2 formula branch, buildCardHtml / emitHiddenFields
- Formula badge in Quotes/Details and Jobs/Details; AI badge gap fixed in Jobs/Details
- Help article (CustomFormulaTemplates.cshtml), Help Index card, HelpController action,
  HelpKnowledgeBase entry; 225/225 unit tests passing

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

src/PowderCoating.Web/Controllers/QuotesController.cs

@@ -2429,6 +2429,25 @@ public class QuotesController : Controller
         var (_, quotePhotoMax) = await _subscriptionService.GetQuotePhotoCountAsync(companyId, 0);
         ViewBag.QuotePhotosEnabled = quotePhotoMax != 0; // 0 = feature disabled for this plan
 
+        var formulaTemplates = await _unitOfWork.CustomItemTemplates.FindAsync(
+            t => t.CompanyId == companyId && t.IsActive);
+        ViewBag.CustomFormulaTemplates = formulaTemplates
+            .OrderBy(t => t.DisplayOrder).ThenBy(t => t.Name)
+            .Select(t => new
+            {
+                id = t.Id,
+                name = t.Name,
+                description = t.Description,
+                outputMode = t.OutputMode,
+                fieldsJson = t.FieldsJson,
+                formula = t.Formula,
+                defaultRate = t.DefaultRate,
+                rateLabel = t.RateLabel,
+                diagramImagePath = string.IsNullOrEmpty(t.DiagramImagePath)
+                    ? (string?)null
+                    : Url.Action("TemplateDiagram", "CompanySettings", new { templateId = t.Id })
+            }).ToList();
+
         // Customers
         var customers = await _unitOfWork.Customers.FindAsync(c => c.CompanyId == companyId);
         ViewBag.Customers = customers