Add workflow templates version tracking to system_stats (#9089)

Adds installed and required workflow templates version information to the
/system_stats endpoint, allowing the frontend to detect and notify users
when their templates package is outdated.

- Add get_installed_templates_version() and get_required_templates_version()
  methods to FrontendManager
- Include templates version info in system_stats response
- Add comprehensive unit tests for the new functionality

server.py

@@ -550,6 +550,8 @@ class PromptServer():
             vram_total, torch_vram_total = comfy.model_management.get_total_memory(device, torch_total_too=True)
             vram_free, torch_vram_free = comfy.model_management.get_free_memory(device, torch_free_too=True)
             required_frontend_version = FrontendManager.get_required_frontend_version()
+            installed_templates_version = FrontendManager.get_installed_templates_version()
+            required_templates_version = FrontendManager.get_required_templates_version()
 
             system_stats = {
                 "system": {
@@ -558,6 +560,8 @@ class PromptServer():
                     "ram_free": ram_free,
                     "comfyui_version": __version__,
                     "required_frontend_version": required_frontend_version,
+                    "installed_templates_version": installed_templates_version,
+                    "required_templates_version": required_templates_version,
                     "python_version": sys.version,
                     "pytorch_version": comfy.model_management.torch_version,
                     "embedded_python": os.path.split(os.path.split(sys.executable)[0])[1] == "python_embeded",