feat(api): implement personalities CRUD API with DTOs and Prisma model

- Add GET /api/personalities?isActive=true|false (list with optional filter)
- Add GET /api/personalities/default (default personality endpoint)
- Add GET /api/personalities/:id (single personality by ID)
- Add POST /api/personalities (create personality)
- Add PATCH /api/personalities/:id (update personality)
- Add DELETE /api/personalities/:id (delete personality)
- Add POST /api/personalities/:id/set-default (convenience set-default)
- Add tone and formalityLevel fields to Prisma Personality model
- Add migration 20260227000000_add_personality_tone_formality
- Map Prisma field names to frontend API contract (systemPrompt->systemPromptTemplate, isEnabled->isActive)
- Apply WorkspaceGuard + PermissionGuard per project patterns
- Return { success: true, data } wrapper for list endpoint
- Add PersonalityQueryDto for isActive filter support
- Update spec files to reflect new field mapping and response shape

Resolves frontend 404 on /api/personalities

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/prisma/migrations/20260227000000_add_personality_tone_formality/migration.sql

@@ -0,0 +1,3 @@
+-- AlterTable: add tone and formality_level columns to personalities
+ALTER TABLE "personalities" ADD COLUMN "tone" TEXT NOT NULL DEFAULT 'neutral';
+ALTER TABLE "personalities" ADD COLUMN "formality_level" "FormalityLevel" NOT NULL DEFAULT 'NEUTRAL';

apps/api/prisma/schema.prisma

@@ -1068,6 +1068,10 @@ model Personality {
   displayName String  @map("display_name")
   description String? @db.Text
 
+  // Tone and formality
+  tone           String         @default("neutral")
+  formalityLevel FormalityLevel @default(NEUTRAL) @map("formality_level")
+
   // System prompt
   systemPrompt String @map("system_prompt") @db.Text