feat: Add Vertex AI Chinese translation support

[Jing-yilin]

Summary

Add complete Chinese localization for KickWatch using Vertex AI to automatically translate all Kickstarter campaign content.

Changes

Backend

• ✅ Add name_zh, blurb_zh, creator_name_zh fields to Campaign model
• ✅ Add name_zh field to Category model
• ✅ Integrate Vertex AI Gemini 2.0 Flash translation service
• ✅ Auto-translate during nightly crawl and backfill
• ✅ All 26 categories with hardcoded Chinese names
• ✅ Batch translation optimization (10 campaigns/batch) for cost savings

Infrastructure

• ✅ GCP Project: rescience-lab-465304
• ✅ Service Account: kickwatch-translator@rescience-lab-465304.iam.gserviceaccount.com
• ✅ AWS Secrets Manager configured:
  • kickwatch-dev/google-service-account (credentials)
  • kickwatch-dev/vertex-ai-config (project config)

Cost Control

• 💰 Uses $1,773 GCP startup credits
• 📊 Batch translation reduces API calls
• ⚡ Fast model (gemini-2.0-flash-exp) for cost efficiency

Deployment Configuration

Add these environment variables to ECS task definition:

{
  "name": "VERTEX_AI_PROJECT_ID",
  "value": "rescience-lab-465304"
},
{
  "name": "VERTEX_AI_LOCATION",
  "value": "us-central1"
},
{
  "name": "GOOGLE_SERVICE_ACCOUNT_JSON",
  "valueFrom": "arn:aws:secretsmanager:us-east-2:739654145647:secret:kickwatch-dev/google-service-account"
}

TODO

• iOS frontend adaptation (display Chinese fields)
• Update GitHub Actions workflow with env vars
• UI text localization (buttons, labels)
• Test translation quality

Testing Plan

1. Local test translation service
2. Run nightly crawl in dev environment
3. Verify Chinese fields populated in database
4. iOS frontend verification

Co-Authored-By: Claude Sonnet 4.5 noreply@anthropic.com

[Jing-yilin]

1. P1 - ios/KickWatch/Tests/MockAPIClient.swift:102

The new CampaignDTO initializer now requires name_zh, blurb_zh, and creator_name_zh, but the shared test factory was not updated. As a result the iOS test target does not compile anymore. Repro:

cd ios && xcodegen generate
xcodebuild test -project KickWatch.xcodeproj -scheme KickWatch -destination "platform=iOS Simulator,name=iPhone 17,OS=26.2" CODE_SIGNING_ALLOWED=NO DEVELOPMENT_TEAM=7Q28CBP3S5

That fails with missing arguments for parameters 'name_zh', 'blurb_zh', 'creator_name_zh' in call from MockAPIClient.swift.

2. P1 - ios/KickWatch/Sources/Services/APIClient.swift:41-61, backend/internal/model/model.go:13-26,57

The Chinese-first fallback currently uses nil-coalescing (name_zh ?? name, etc.), but the backend model fields are plain Go strings. For untranslated rows JSON will contain empty strings, not null, and Swift decodes "" into a non-nil String?. That means existing campaigns/categories without a translation will prefer the empty localized field over the English one, so names can render blank and creator rows can become by until every record is backfilled. The fallback needs to treat empty strings as missing.

3. P2 - backend/internal/service/cron.go:84-88

syncCategories() still only upserts name and parent_id. Because ListCategories() serves directly from the DB once any category rows exist, upgraded environments with already-seeded categories will never get name_zh populated, so the new localized category chips will not show up there.

Test results:

• cd backend && go test ./... ✅
• iOS unit tests/build ❌ (compile failure above)