fix: constrain OS icon sizing and remove background when image loads

- Add overflow:hidden to .vf-os-card and .vf-os-icon
- Constrain .vf-os-icon img with max-width/max-height:100%
- Only apply brand color background as fallback when image fails to load
- No background color when image is present (clean transparent display)
- Apply same logic to both category headers and template cards
- Update both module.js (rebuild panel) and hooks.php (checkout page)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

modules/servers/VirtFusionDirect/templates/css/module.css

@@ -302,6 +302,7 @@
     padding: 10px 8px;
     text-align: center;
     cursor: pointer;
+    overflow: hidden;
     transition: border-color 0.15s, background-color 0.15s, box-shadow 0.15s;
 }
 .vf-os-card:hover {
@@ -326,8 +327,12 @@
     color: #fff;
     font-weight: 700;
     font-size: 1.1rem;
+    overflow: hidden;
+    flex-shrink: 0;
 }
 .vf-os-icon img {
+    max-width: 100%;
+    max-height: 100%;
     width: 24px;
     height: 24px;
     object-fit: contain;