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/storage/template.py

@@ -0,0 +1,61 @@
+"""Capture template data model."""
+
+from dataclasses import dataclass
+from datetime import datetime
+from typing import Any, Dict, Optional
+
+
+@dataclass
+class CaptureTemplate:
+    """Represents a screen capture template configuration."""
+
+    id: str
+    name: str
+    engine_type: str
+    engine_config: Dict[str, Any]
+    is_default: bool
+    created_at: datetime
+    updated_at: datetime
+    description: Optional[str] = None
+
+    def to_dict(self) -> dict:
+        """Convert template to dictionary.
+
+        Returns:
+            Dictionary representation
+        """
+        return {
+            "id": self.id,
+            "name": self.name,
+            "engine_type": self.engine_type,
+            "engine_config": self.engine_config,
+            "is_default": self.is_default,
+            "created_at": self.created_at.isoformat(),
+            "updated_at": self.updated_at.isoformat(),
+            "description": self.description,
+        }
+
+    @classmethod
+    def from_dict(cls, data: dict) -> "CaptureTemplate":
+        """Create template from dictionary.
+
+        Args:
+            data: Dictionary with template data
+
+        Returns:
+            CaptureTemplate instance
+        """
+        return cls(
+            id=data["id"],
+            name=data["name"],
+            engine_type=data["engine_type"],
+            engine_config=data.get("engine_config", {}),
+            is_default=data.get("is_default", False),
+            created_at=datetime.fromisoformat(data["created_at"])
+            if isinstance(data.get("created_at"), str)
+            else data.get("created_at", datetime.utcnow()),
+            updated_at=datetime.fromisoformat(data["updated_at"])
+            if isinstance(data.get("updated_at"), str)
+            else data.get("updated_at", datetime.utcnow()),
+            description=data.get("description"),
+        )