Change form input backgrounds to solid black sitewide

Updated global form styles in main.scss and mortgage calculator inputs
to use #000 background instead of color variables.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

wp-content/themes/homeproz/src/main.scss

@@ -227,7 +227,7 @@ textarea,
 select {
     width: 100%;
     padding: 0.75rem 1rem;
-    background-color: var(--color-bg-card);
+    background-color: #000;
     border: 1px solid var(--color-border);
     border-radius: 0.25rem;
     color: var(--color-text);

wp-content/themes/homeproz/template-parts/content/content-mortgage-calculator.scss

@@ -85,7 +85,7 @@
     select {
         width: 100%;
         padding: 0.75rem 1rem;
-        background-color: var(--color-bg-dark);
+        background-color: #000;
         border: 1px solid var(--color-border);
         border-radius: 0.25rem;
         color: var(--color-text);