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/core/capture_engines/base.py

@@ -35,7 +35,7 @@ class CaptureEngine(ABC):
     """Abstract base class for screen capture engines.
 
     All screen capture engines must implement this interface to be
-    compatible with the WLED Screen Controller system.
+    compatible with the WLED Grab system.
     """
 
     ENGINE_TYPE: str = "base"  # Override in subclasses