Add Picture Streams architecture with postprocessing templates and stream test UI

Introduce Picture Stream abstraction that separates the capture pipeline into
composable layers: raw streams (display + capture engine + FPS) and processed
streams (source stream + postprocessing template). Devices reference a picture
stream instead of managing individual capture settings.

- Add PictureStream and PostprocessingTemplate data models and stores
- Add CRUD API endpoints for picture streams and postprocessing templates
- Add stream chain resolution in ProcessorManager for start_processing
- Add picture stream test endpoint with postprocessing preview support
- Add Stream Settings modal with border_width and interpolation_mode controls
- Add stream test modal with capture preview and performance metrics
- Add full frontend: Picture Streams tab, Processing Templates tab, stream
  selector on device cards, test buttons on stream cards
- Add localization keys for all new features (en, ru)
- Migrate existing devices to picture streams on startup

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

server/src/wled_controller/static/style.css

@@ -1762,24 +1762,6 @@ input:-webkit-autofill:focus {
     gap: 20px;
 }
 
-.templates-separator {
-    grid-column: 1 / -1;
-    display: flex;
-    align-items: center;
-    gap: 12px;
-    color: var(--text-secondary);
-    font-size: 0.85rem;
-    font-weight: 500;
-}
-
-.templates-separator::before,
-.templates-separator::after {
-    content: '';
-    flex: 1;
-    height: 1px;
-    background: var(--border-color);
-}
-
 .template-card {
     background: var(--card-bg);
     border: 1px solid var(--border-color);
@@ -1839,7 +1821,7 @@ input:-webkit-autofill:focus {
     margin-bottom: 12px;
 }
 
-.template-card:has(.card-remove-btn) .template-card-header {
+.template-card .template-card-header {
     padding-right: 24px;
 }
 
@@ -1857,11 +1839,6 @@ input:-webkit-autofill:focus {
     text-transform: uppercase;
 }
 
-.badge-default {
-    background: var(--primary-color);
-    color: white;
-}
-
 .template-description {
     color: var(--text-secondary);
     font-size: 14px;
@@ -2038,6 +2015,36 @@ input:-webkit-autofill:focus {
     font-size: 16px;
 }
 
+/* Stream type badges */
+.badge-raw {
+    background: #1976d2;
+    color: white;
+}
+
+.badge-processed {
+    background: #7b1fa2;
+    color: white;
+}
+
+/* Stream info panel in stream selector modal */
+.stream-info-panel {
+    background: var(--bg-secondary, #2a2a2a);
+    border: 1px solid var(--border-color);
+    border-radius: 8px;
+    padding: 12px 16px;
+    margin-top: 12px;
+    font-size: 14px;
+    line-height: 1.6;
+}
+
+.stream-info-panel div {
+    margin-bottom: 4px;
+}
+
+.stream-info-panel strong {
+    margin-right: 6px;
+}
+
 /* Responsive adjustments */
 @media (max-width: 768px) {
     .templates-grid {