fix: add missing invalid_host error string to strings.json

config_flow.py sets errors = {"base": "invalid_host"} when bridge
discovery returns no results, but the key was not defined in strings.json
causing the error to be silently swallowed with no user feedback.

Relates to #141

Author: jensihnow

custom_components/comfoconnect/strings.json

@@ -33,7 +33,8 @@
   },
   "config": {
     "error": {
-      "invalid_pin": "Invalid PIN"
+      "invalid_pin": "Invalid PIN",
+      "invalid_host": "Could not find a ComfoConnect bridge at this address"
     },
     "step": {
       "user": {