feat(08-03): FavoriteLink schema + FavoritesModule (CRUD + SSRF icon discovery)

- Add FavoriteLink Prisma model (userId/tenantId/widgetId scope, iconUrl nullable, position)
- IconDiscoveryService: port SSRF-protected icon discovery with redirect: 'manual',
  private IP / blocked-hostname checks, 4000ms timeout, 200k HTML cap (T-08-05)
- FavoritesService: list/create/update/remove all scoped by userId (T-08-06 / Pitfall 3)
- FavoritesController: GET /favorites?widgetId, POST, PATCH :id, DELETE :id
- FavoritesModule registered in AppModule
- tsc --noEmit passes for @tessera/api

apps/api/prisma/schema.prisma

@@ -233,3 +233,20 @@ model SmtpConfig {
   createdAt         DateTime @default(now())
   updatedAt         DateTime @updatedAt
 }
+
+model FavoriteLink {
+  id        String   @id @default(uuid())
+  userId    String
+  tenantId  String
+  widgetId  String
+  title     String
+  url       String
+  iconUrl   String?
+  position  Int      @default(0)
+  createdAt DateTime @default(now())
+  updatedAt DateTime @updatedAt
+
+  @@index([userId])
+  @@index([tenantId])
+  @@index([widgetId])
+}