Add static image picture stream type with auto-validating UI

Introduces a new "static_image" stream type that loads a frame from a URL
or local file path, enabling LED testing with known images or displaying
static content. Includes validate-image API endpoint, auto-validation on
blur/enter/paste with caching, capture template names on stream cards,
and conditional test stats display for single-frame results.

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

server/src/wled_controller/static/style.css

@@ -2360,3 +2360,45 @@ input:-webkit-autofill:focus {
     }
 }
 
+/* Static image stream styles */
+.image-preview-container {
+    text-align: center;
+    margin: 12px 0;
+    padding: 12px;
+    background: var(--bg-secondary);
+    border-radius: 8px;
+    border: 1px solid var(--border-color);
+}
+.stream-image-preview {
+    max-width: 100%;
+    max-height: 200px;
+    border-radius: 4px;
+    border: 1px solid var(--border-color);
+}
+.stream-image-info {
+    font-size: 0.75rem;
+    color: var(--text-muted);
+    margin-top: 6px;
+}
+.validation-status {
+    font-size: 0.8rem;
+    margin-top: 4px;
+    padding: 4px 8px;
+    border-radius: 4px;
+}
+.validation-status.success {
+    color: #4caf50;
+}
+.validation-status.error {
+    color: #f44336;
+}
+.validation-status.loading {
+    color: var(--text-muted);
+}
+.stream-card-image-source {
+    font-size: 0.7rem;
+    color: var(--text-muted);
+    word-break: break-all;
+    margin-top: 4px;
+}
+