feat(service-integrations): phase 1 — integration architecture foundation

- Add Integration interfaces, registry, cache, encryption, and base helpers
- Add integrationType, integrationConfig, integrationEnabled to App model
- Add integration widget type to constants and validators
- Add integration fields to AppRecord, CreateAppInput, UpdateAppInput
- Update appService with encryption/decryption for integration config
- Add API routes: list integrations, test connection, fetch endpoint data

prisma/schema.prisma

@@ -80,6 +80,9 @@ model App {
   healthcheckMethod       String   @default("GET")
   healthcheckExpectedStatus Int    @default(200)
   healthcheckTimeout      Int      @default(5000) // milliseconds
+  integrationType         String?
+  integrationConfig       String?
+  integrationEnabled      Boolean  @default(false)
   createdById             String?
   createdAt               DateTime @default(now())
   updatedAt               DateTime @updatedAt