feat(#135): implement Quality Gate Configuration System

Add database-backed quality gate configuration for workspaces with
full CRUD operations and default gate seeding.

Schema:
- Add QualityGate model with workspace relation
- Support for custom commands and regex patterns
- Enable/disable and ordering support

Service:
- CRUD operations for quality gates
- findEnabled: Get ordered, enabled gates
- reorder: Bulk reorder with transaction
- seedDefaults: Seed 4 default gates
- toOrchestratorFormat: Convert to orchestrator interface

Endpoints:
- GET /workspaces/:id/quality-gates - List
- GET /workspaces/:id/quality-gates/:gateId - Get one
- POST /workspaces/:id/quality-gates - Create
- PATCH /workspaces/:id/quality-gates/:gateId - Update
- DELETE /workspaces/:id/quality-gates/:gateId - Delete
- POST /workspaces/:id/quality-gates/reorder
- POST /workspaces/:id/quality-gates/seed-defaults

Default gates: Build, Lint, Test, Coverage (85%)

Tests: 25 passing with 95.16% coverage

Fixes #135

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/prisma/schema.prisma

@@ -215,6 +215,7 @@ model Workspace {
   cronSchedules    CronSchedule[]
   personalities    Personality[]
   llmSettings      WorkspaceLlmSettings?
+  qualityGates     QualityGate[]
 
   @@index([ownerId])
   @@map("workspaces")
@@ -1003,3 +1004,29 @@ model WorkspaceLlmSettings {
   @@index([defaultPersonalityId])
   @@map("workspace_llm_settings")
 }
+
+// ============================================
+// QUALITY GATE MODULE
+// ============================================
+
+model QualityGate {
+  id             String   @id @default(uuid()) @db.Uuid
+  workspaceId    String   @map("workspace_id") @db.Uuid
+  workspace      Workspace @relation(fields: [workspaceId], references: [id], onDelete: Cascade)
+  name           String
+  description    String?
+  type           String   // 'build' | 'lint' | 'test' | 'coverage' | 'custom'
+  command        String?
+  expectedOutput String?  @map("expected_output")
+  isRegex        Boolean  @default(false) @map("is_regex")
+  required       Boolean  @default(true)
+  order          Int      @default(0)
+  isEnabled      Boolean  @default(true) @map("is_enabled")
+  createdAt      DateTime @default(now()) @map("created_at") @db.Timestamptz
+  updatedAt      DateTime @updatedAt @map("updated_at") @db.Timestamptz
+
+  @@unique([workspaceId, name])
+  @@index([workspaceId])
+  @@index([workspaceId, isEnabled])
+  @@map("quality_gates")
+}