Merge templates into Streams tab, rename app to WLED Grab

- Merge Capture Templates and Processing Templates main tabs into Picture
  Streams sub-tabs (Screen Capture shows streams + engine templates,
  Processed shows streams + filter templates)
- Rename "Capture Templates" to "Engine Templates" and "Processing
  Templates" to "Filter Templates" across all locale strings
- Rename "Picture Streams" tab to "Streams" throughout UI and locales
- Rename "WLED Screen Controller" to "WLED Grab" across all files
- Add subtab section headers and styling for merged template views
- Remove add card labels, keeping only plus icon for cleaner UI

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

server/src/wled_controller/static/style.css

@@ -2230,6 +2230,24 @@ input:-webkit-autofill:focus {
     display: block;
 }
 
+/* Sub-tab content sections */
+.subtab-section {
+    margin-bottom: 24px;
+}
+
+.subtab-section:last-child {
+    margin-bottom: 0;
+}
+
+.subtab-section-header {
+    font-size: 1rem;
+    font-weight: 600;
+    color: var(--text-secondary);
+    margin: 0 0 12px 0;
+    padding-bottom: 8px;
+    border-bottom: 1px solid var(--border-color);
+}
+
 /* Image Lightbox */
 .lightbox {
     display: none;