feat(api): implement personalities CRUD API (#537)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.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