Enhance NPC creation functionality and validation in Admin module

- Updated AdminController to validate the count parameter, ensuring it is between 1 and 500.
- Refactored NPC creation logic in AdminService to create NPCs for each city-title combination, improving efficiency.
- Enhanced frontend localization files to reflect changes in count descriptions and validation messages.
- Updated CreateNPCView to provide user guidance on count input and display detailed creation results.

frontend/src/i18n/locales/en/admin.json

@@ -149,18 +149,20 @@
                 "to": "to",
                 "years": "years",
                 "titleRange": "Title Range",
-                "count": "Count",
+                "count": "Count per City-Title Combination",
+                "countHelp": "This count will be created for each combination of selected city and title.",
                 "create": "Create NPCs",
                 "creating": "Creating...",
                 "result": "Result",
                 "createdCount": "{count} NPCs have been created.",
+                "combinationInfo": "{perCombination} NPCs per combination × {combinations} combinations = {count} NPCs total",
                 "age": "Age",
                 "errorLoadingRegions": "Error loading cities.",
                 "errorLoadingTitles": "Error loading titles.",
                 "errorCreating": "Error creating NPCs.",
                 "invalidAgeRange": "Invalid age range.",
                 "invalidTitleRange": "Invalid title range.",
-                "invalidCount": "Invalid count (1-100)."
+                "invalidCount": "Invalid count (1-500)."
             }
         },
         "chatrooms": {