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/dto/update-personality.dto.ts

@@ -1,4 +1,38 @@
-import { PartialType } from "@nestjs/mapped-types";
-import { CreatePersonalityDto } from "./create-personality.dto";
+import { IsString, IsOptional, IsBoolean, MinLength, MaxLength, IsIn } from "class-validator";
+import { FORMALITY_LEVELS, FormalityLevelType } from "./create-personality.dto";
 
-export class UpdatePersonalityDto extends PartialType(CreatePersonalityDto) {}
+export class UpdatePersonalityDto {
+  @IsOptional()
+  @IsString()
+  @MinLength(1)
+  @MaxLength(100)
+  name?: string;
+
+  @IsOptional()
+  @IsString()
+  @MaxLength(500)
+  description?: string;
+
+  @IsOptional()
+  @IsString()
+  @MinLength(1)
+  @MaxLength(50)
+  tone?: string;
+
+  @IsOptional()
+  @IsIn(FORMALITY_LEVELS)
+  formalityLevel?: FormalityLevelType;
+
+  @IsOptional()
+  @IsString()
+  @MinLength(10)
+  systemPromptTemplate?: string;
+
+  @IsOptional()
+  @IsBoolean()
+  isDefault?: boolean;
+
+  @IsOptional()
+  @IsBoolean()
+  isActive?: boolean;
+}