Fix MSS template test: add engine initialization and create TemplateStore

- Add engine.initialize() call in test endpoint to fix "Engine not initialized" error for MSS and DXcam
- Create template.py with CaptureTemplate dataclass for template data model
- Create template_store.py with TemplateStore class for template CRUD operations
- TemplateStore loads from capture_templates.json and provides get_all, create, get, update, delete methods

Fixes MSS capture test failing with "Engine not initialized" error. WGC worked because it auto-initializes in capture_display(), but MSS and DXcam require explicit initialization.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

server/src/wled_controller/api/routes.py

@@ -930,8 +930,9 @@ async def test_template(
                 )
             )
 
-        # Create engine (initialization happens on first capture)
+        # Create and initialize engine
         engine = EngineRegistry.create_engine(test_request.engine_type, test_request.engine_config)
+        engine.initialize()
 
         # Run sustained capture test
         logger.info(f"Starting {test_request.capture_duration}s capture test with {test_request.engine_type}")