Inline item editing on Job Details with live pricing and costing updates

- PatchItem: add case-insensitive JSON deserialization; add legacy fallback
  that computes a live breakdown from job items when PricingBreakdownJson is null
- PatchItem: return itemsSubtotal, subtotalBeforeDiscount, subtotalAfterDiscount,
  taxAmount in JSON response for immediate DOM updates
- GetCostingBreakdown: use job.FinalPrice as revenue (not invoice total) so
  costing figures reflect inline edits before an invoice exists
- Details.cshtml: add data-pb attributes to visible pricing rows; add
  job-final-price-display class to visible Total element
- Details.cshtml: wire afterSave callback to call costing.load() after each edit
- inline-item-edit.js: add afterSave hook in commit(); clean up debug logging
- Help docs: add Inline Price Editing sections to Jobs, Quotes, and Invoices
  help articles; add inline editing + job costing revenue notes to AI knowledge base

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

src/PowderCoating.Web/Views/Help/Quotes.cshtml

@@ -213,6 +213,25 @@
             </div>
         </section>
 
+        <section id="inline-price-editing" class="mb-5">
+            <h2 class="h4 fw-bold border-bottom pb-2 mb-3">
+                <i class="bi bi-pencil-square text-primary me-2"></i>Inline Price Editing
+            </h2>
+            <p>
+                On the Quote Details page you can edit any item&rsquo;s unit price, quantity, or
+                description directly in the table without opening the full Edit form.
+            </p>
+            <ol class="mb-3">
+                <li class="mb-2">Click a <strong>unit price</strong>, <strong>quantity</strong>, or <strong>description</strong> cell in the Items table. The cell turns into an input field.</li>
+                <li class="mb-2">Type the new value.</li>
+                <li class="mb-2">Press <kbd>Enter</kbd> or click outside the field to save. Press <kbd>Esc</kbd> to cancel without saving.</li>
+            </ol>
+            <p>
+                The pricing summary (subtotal, discount, tax, and grand total) updates immediately
+                &mdash; no page reload required.
+            </p>
+        </section>
+
         <section id="quote-statuses" class="mb-5">
             <h2 class="h4 fw-bold border-bottom pb-2 mb-3">
                 <i class="bi bi-tag text-primary me-2"></i>Quote Statuses