Disable Sentry in CI, tag environment correctly

Client: VITE_SENTRY_ENVIRONMENT=ci baked in during CI build, disables
Sentry and sets 0 sample rates. Server: checks process.env.CI to
disable and tag as "ci" environment.

Production remains enabled with "production" environment tag.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -177,6 +177,8 @@ jobs:
 
       - name: Build for production
         run: pnpm build
+        env:
+          VITE_SENTRY_ENVIRONMENT: ci
 
       - name: Run E2E tests
         run: pnpm test:e2e