feat(#82): add prompt formatter service to personality module

- Add PromptFormatterService for formatting system prompts based on personality
- Support context variable interpolation (userName, workspaceName, etc.)
- Add formality level modifiers (VERY_CASUAL to VERY_FORMAL)
- Add template validation for custom variables
- Add preview endpoint for formatted prompts
- Fix UpdatePersonalityDto to avoid @nestjs/mapped-types dependency
- Update PersonalitiesController with new endpoints
- Add comprehensive tests (33 passing tests)

Closes #82

apps/api/src/personalities/personalities.module.ts

@@ -3,11 +3,12 @@ import { PrismaModule } from "../prisma/prisma.module";
 import { AuthModule } from "../auth/auth.module";
 import { PersonalitiesService } from "./personalities.service";
 import { PersonalitiesController } from "./personalities.controller";
+import { PromptFormatterService } from "./services/prompt-formatter.service";
 
 @Module({
   imports: [PrismaModule, AuthModule],
   controllers: [PersonalitiesController],
-  providers: [PersonalitiesService],
-  exports: [PersonalitiesService],
+  providers: [PersonalitiesService, PromptFormatterService],
+  exports: [PersonalitiesService, PromptFormatterService],
 })
 export class PersonalitiesModule {}