Fix flat-rate coat wizard UX, — literal, select caret overlap, and walkthrough modal sizing

- Flat-rate items now default coat type to Custom so Color Name field is immediately visible
- Catalog search blur copies typed text to Color Name when no catalog result was selected
- Item card shows 'No color specified' badge when coat has powder-to-order but no color name
- Color Name label marked required with '(shows on quote)' hint
- Coat name select min-width prevents text overlapping Bootstrap caret arrow
- Remove extra unbalanced </div> from renderSalesFields
- Fix literal &mdash; in quote simple-mode hint (textContent → innerHTML)
- Formula walkthrough modal fixed at 700px so all steps render at identical window size

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

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

@@ -590,7 +590,7 @@
             function applyMode(mode) {
                 if (mode === 'simple') {
                     form.classList.add('quote-simple-mode');
-                    hint.textContent = 'Advanced fields are hidden — switch to Full Quote to see them.';
+                    hint.innerHTML = 'Advanced fields are hidden — switch to Full Quote to see them.';
                 } else {
                     form.classList.remove('quote-simple-mode');
                     hint.textContent = '';